Compound interest calculator guide
What is a Compound Interest Calculator?
A Compound Interest Calculator estimates how an investment or deposit grows over time when the interest you earn is added back to the principal. You enter the starting amount, the annual interest rate, the number of years and how often interest is compounded. The calculator then shows the maturity value, the total interest earned and how much of the final amount came from compounding rather than your original money.
Compounding is the reason a small monthly SIP or a long-term PPF deposit can grow into a large corpus. The earlier you start and the longer you stay invested, the more the later years contribute. This page explains the formula, the effect of compounding frequency and how to read the result so you can plan realistic goals.
The output is a mathematical estimate. Actual returns from mutual funds or stocks are not fixed and can go up or down. For fixed deposits and small savings schemes, the rate is known in advance, but taxes and premature withdrawal rules can change the final in-hand amount.
What this calculator shows you
- Principal — the amount you start with.
- Total interest earned — the difference between the maturity value and the principal.
- Maturity value — principal plus all compounded interest.
- Year-wise growth — how the balance rises each year and how the interest component accelerates.
- Effect of compounding frequency — yearly, half-yearly, quarterly or monthly compounding changes the effective annual yield.
- Additional contributions — many calculators let you add a monthly or yearly contribution, which is the SIP mode.
- Effective annual rate — the actual annual return after taking compounding into account.
Tip: Compounding rewards time more than timing. A 10-year delay can cut the final corpus by more than half, even if you invest the same total amount later. Run a shorter tenure and a longer tenure side by side to see the difference.
How to use the compound interest calculator
- Enter the principal — your lump sum or initial investment.
- Enter the annual interest rate. For fixed deposits, use the contracted rate. For equity, use a conservative long-term assumption.
- Enter the tenure in years.
- Choose the compounding frequency — yearly, half-yearly, quarterly or monthly. Fixed deposits usually compound quarterly; many savings accounts compound daily or monthly.
- If you are investing regularly, add the monthly or yearly contribution in the SIP or recurring deposit field.
- Read the maturity value and the total interest.
- Change one input at a time — extend the tenure by five years, or increase the rate by 1% — and watch the maturity value move.
Compound interest formula
A = P × (1 + r/n)n×t
- A — maturity value (principal + interest)
- P — principal
- r — annual interest rate in decimal (for 8%, use 0.08)
- n — number of times interest is compounded per year
- t — tenure in years
For monthly contributions, the formula is applied to each instalment separately and then summed. Most online calculators handle this internally. If you are calculating by hand, treat each SIP instalment as a separate lump sum invested for the remaining months.
The formula assumes the rate stays constant and interest is reinvested. In real life, fixed deposit rates change on renewal, and market-linked returns fluctuate.
Compounding frequency matters
Frequency
n
Effect on maturity
Yearly 1 Lowest among the options for the same rate Half-yearly 2 Slightly higher than yearly Quarterly 4 Common for fixed deposits; higher than half-yearly Monthly 12 Higher still; used by many recurring deposits Daily 365 Close to continuous compounding; highest for the same rate
A fixed deposit advertised at 8% per year compounds quarterly, so the effective annual yield is about 8.24%. A savings account at 4% compounded daily gives an effective yield of about 4.08%. The difference looks small on a single year, but over 20 years it becomes significant.
When you compare two fixed deposits, compare the effective annual yield, not just the headline rate. The compounding frequency is part of the offer.
Simple vs compound interest
Point
Simple interest
Compound interest
Basis
Interest only on the original principal
Interest on principal plus accumulated interest
Formula
SI = P × r × t
A = P × (1 + r/n)n×t
Growth
Linear
Exponential over long periods
Common use
Some short-term loans, simple interest bonds
Fixed deposits, PPF, mutual funds, most savings products
Over a 20-year horizon, the gap between simple and compound interest at the same rate is large. A ₹1,00,000 deposit at 8% simple interest grows to ₹2,60,000 in 20 years. At 8% compounded yearly, it grows to about ₹4,66,000. At quarterly compounding, slightly more.
Illustrative examples
Sample maths only. Actual returns may differ.
Principal
Rate
Tenure
Compounding
Approx. maturity
Approx. interest
₹1,00,000
8%
10 years
Yearly
≈ ₹2,15,900
≈ ₹1,15,900
₹1,00,000
8%
20 years
Yearly
≈ ₹4,66,100
≈ ₹3,66,100
₹5,00,000
7%
15 years
Quarterly
≈ ₹14,20,000
≈ ₹9,20,000
₹10,000 monthly SIP
12%
15 years
Monthly
≈ ₹50,45,000
≈ ₹32,45,000
The SIP example shows the same principle: regular investing plus compounding can build a large corpus even if each instalment is modest. Use the SIP Calculator for a detailed month-by-month projection.
How to read the result
- Maturity value — the total amount you receive if you stay invested for the full tenure and the rate does not change.
- Total interest — the gain from compounding. It is not the same as the annual interest multiplied by the number of years.
- Principal share — in long tenures, the interest component often exceeds the principal. That is normal.
- Effective annual rate — use this to compare products with different compounding frequencies.
- Year-wise table — shows how the interest earned each year starts small and grows. This is the power of compounding in action.
- Post-tax value — most calculators show pre-tax figures. Interest on fixed deposits is taxable at your slab rate. Deduct tax to get the in-hand amount.
Rule of 72
The Rule of 72 is a quick way to estimate how long an investment takes to double. Divide 72 by the annual rate of return. At 8%, money doubles in roughly 72 ÷ 8 = 9 years. At 12%, it doubles in about 6 years. At 6%, it takes about 12 years.
This rule assumes yearly compounding and a constant rate. It is an approximation, but it is useful for quick mental maths. For exact figures, use the calculator.
Compounding and inflation
Compounding works both ways. Inflation compounds too, which means the cost of living rises exponentially over time. A 6% inflation rate halves the purchasing power of money in about 12 years. That is why an investment that only matches inflation does not build real wealth.
Your real return is the nominal return minus inflation. If a fixed deposit gives 7% and inflation is 6%, the real return is about 1%. Over 20 years, that barely grows your purchasing power. Use the Inflation Calculator to see how prices may change, and the Retirement Planning Calculator to plan a corpus that keeps pace.
Common mistakes to avoid
- Ignoring compounding frequency. Two deposits with the same headline rate can give different returns if one compounds quarterly and the other yearly.
- Using an unrealistic rate. Equity returns are not fixed. Test a lower rate as well as a higher one.
- Forgetting tax. Interest on fixed deposits is added to your income and taxed at your slab rate. TDS may apply if interest exceeds the threshold.
- Stopping early. The last few years of a long tenure contribute the largest absolute gains. Premature withdrawal can cut the maturity value sharply.
- Comparing a compounded product with a simple-interest product on headline rate alone. Compare effective annual yield.
- Not accounting for inflation. A large nominal corpus may not be enough in real terms after 20 years.
- Assuming the calculator includes fees or expense ratios. Mutual fund returns are shown net of expenses, but other products may have charges not reflected here.
Frequently asked questions
What is the difference between compound interest and simple interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus the interest already earned. Over long periods, compound interest produces much higher maturity values.
Which compounding frequency is best for me?
More frequent compounding gives a slightly higher effective yield for the same headline rate. But the difference is small. The bigger factors are the rate, the tenure and whether you keep reinvesting. Choose a product that matches your liquidity needs and tax situation.
Does this calculator work for SIPs?
Many compound interest calculators have an SIP mode where you enter a monthly contribution. If yours does not, use the SIP Calculator. The underlying maths is the same: each instalment compounds for the remaining period.
Is the maturity value guaranteed?
Only for fixed deposits and small savings schemes where the rate is contracted. For market-linked investments such as mutual funds, the value can go up or down. The calculator assumes a constant rate for illustration.
How is interest on fixed deposits taxed?
Interest is added to your total income and taxed at your slab rate. Banks deduct TDS if interest exceeds the notified threshold in a financial year. Senior citizens have a higher TDS threshold and a deduction under Section 80TTB. Use the Income Tax Calculator to estimate your liability.
Can I use this for PPF or EPF?
Yes. PPF and EPF have a notified rate that is compounded yearly. Enter the rate, the yearly contribution and the tenure. The PPF Calculator is built specifically for that scheme and handles the 15-year lock-in and extension rules.
What rate should I assume for equity mutual funds?
There is no guaranteed rate. Many planners use 10–12% for long-term equity, but actual returns vary widely. Run the calculator at 8%, 10% and 12% to see a range of outcomes. Do not plan on the highest number alone.
Why is the interest in later years so much larger?
Because the base on which interest is calculated has grown. Each year’s interest is added to the principal, so the next year earns interest on a larger amount. This is the compounding effect.
Does the calculator account for inflation?
No. It shows nominal values. To see real purchasing power, subtract inflation from the return or use the Inflation Calculator.
Related calculators
SIP Calculator
PPF Calculator
Retirement Planning Calculator
Inflation Calculator
Income Tax Calculator
Salary Calculator
Home Loan Calculator
EMI Calculator
Loan Calculator
Related guides
Personal Finance Calculator Guide
Wealth Creation Strategy in India
KCC Loan 2026: Limit, Rate and Rules
Checklist for compound interest planning
- Tenure and rate tested together — not just the headline rate
- Compounding frequency checked for the product you are comparing
- Tax on interest estimated before you finalise the plan
- Inflation-adjusted real return calculated for long goals
- Emergency fund kept separate from long-term investments
- Regular contributions increased each year where possible
- Premature withdrawal penalties and lock-in periods read
- Projection reviewed at least once a year
Disclaimer: This compound interest calculator and the content on this page are for education and mathematical estimation only. They are not investment advice, a guarantee of returns, or a substitute for professional consultation. Market-linked investments carry risk, and fixed-deposit rates change on renewal. Tax treatment depends on your income slab and the current provisions of the Income-tax Act. Results depend entirely on the inputs you enter. Verify all rates, fees and tax rules with the product provider or a qualified adviser before you invest. Harshonomics is not a lender, a mutual fund distributor, or a SEBI-registered Investment Adviser.
Compound interest calculator guide
What is a Compound Interest Calculator?
A Compound Interest Calculator estimates how an investment or deposit grows over time when the interest you earn is added back to the principal. You enter the starting amount, the annual interest rate, the number of years and how often interest is compounded. The calculator then shows the maturity value, the total interest earned and how much of the final amount came from compounding rather than your original money.
Compounding is the reason a small monthly SIP or a long-term PPF deposit can grow into a large corpus. The earlier you start and the longer you stay invested, the more the later years contribute. This page explains the formula, the effect of compounding frequency and how to read the result so you can plan realistic goals.
The output is a mathematical estimate. Actual returns from mutual funds or stocks are not fixed and can go up or down. For fixed deposits and small savings schemes, the rate is known in advance, but taxes and premature withdrawal rules can change the final in-hand amount.
What this calculator shows you
- Principal — the amount you start with.
- Total interest earned — the difference between the maturity value and the principal.
- Maturity value — principal plus all compounded interest.
- Year-wise growth — how the balance rises each year and how the interest component accelerates.
- Effect of compounding frequency — yearly, half-yearly, quarterly or monthly compounding changes the effective annual yield.
- Additional contributions — many calculators let you add a monthly or yearly contribution, which is the SIP mode.
- Effective annual rate — the actual annual return after taking compounding into account.
Tip: Compounding rewards time more than timing. A 10-year delay can cut the final corpus by more than half, even if you invest the same total amount later. Run a shorter tenure and a longer tenure side by side to see the difference.
How to use the compound interest calculator
- Enter the principal — your lump sum or initial investment.
- Enter the annual interest rate. For fixed deposits, use the contracted rate. For equity, use a conservative long-term assumption.
- Enter the tenure in years.
- Choose the compounding frequency — yearly, half-yearly, quarterly or monthly. Fixed deposits usually compound quarterly; many savings accounts compound daily or monthly.
- If you are investing regularly, add the monthly or yearly contribution in the SIP or recurring deposit field.
- Read the maturity value and the total interest.
- Change one input at a time — extend the tenure by five years, or increase the rate by 1% — and watch the maturity value move.
Compound interest formula
A = P × (1 + r/n)n×t
- A — maturity value (principal + interest)
- P — principal
- r — annual interest rate in decimal (for 8%, use 0.08)
- n — number of times interest is compounded per year
- t — tenure in years
For monthly contributions, the formula is applied to each instalment separately and then summed. Most online calculators handle this internally. If you are calculating by hand, treat each SIP instalment as a separate lump sum invested for the remaining months.
The formula assumes the rate stays constant and interest is reinvested. In real life, fixed deposit rates change on renewal, and market-linked returns fluctuate.
Compounding frequency matters
| Frequency | n | Effect on maturity |
|---|---|---|
| Yearly | 1 | Lowest among the options for the same rate |
| Half-yearly | 2 | Slightly higher than yearly |
| Quarterly | 4 | Common for fixed deposits; higher than half-yearly |
| Monthly | 12 | Higher still; used by many recurring deposits |
| Daily | 365 | Close to continuous compounding; highest for the same rate |
A fixed deposit advertised at 8% per year compounds quarterly, so the effective annual yield is about 8.24%. A savings account at 4% compounded daily gives an effective yield of about 4.08%. The difference looks small on a single year, but over 20 years it becomes significant.
When you compare two fixed deposits, compare the effective annual yield, not just the headline rate. The compounding frequency is part of the offer.
Simple vs compound interest
| Point | Simple interest | Compound interest |
|---|---|---|
| Basis | Interest only on the original principal | Interest on principal plus accumulated interest |
| Formula | SI = P × r × t | A = P × (1 + r/n)n×t |
| Growth | Linear | Exponential over long periods |
| Common use | Some short-term loans, simple interest bonds | Fixed deposits, PPF, mutual funds, most savings products |
Over a 20-year horizon, the gap between simple and compound interest at the same rate is large. A ₹1,00,000 deposit at 8% simple interest grows to ₹2,60,000 in 20 years. At 8% compounded yearly, it grows to about ₹4,66,000. At quarterly compounding, slightly more.
Illustrative examples
Sample maths only. Actual returns may differ.
| Principal | Rate | Tenure | Compounding | Approx. maturity | Approx. interest |
|---|---|---|---|---|---|
| ₹1,00,000 | 8% | 10 years | Yearly | ≈ ₹2,15,900 | ≈ ₹1,15,900 |
| ₹1,00,000 | 8% | 20 years | Yearly | ≈ ₹4,66,100 | ≈ ₹3,66,100 |
| ₹5,00,000 | 7% | 15 years | Quarterly | ≈ ₹14,20,000 | ≈ ₹9,20,000 |
| ₹10,000 monthly SIP | 12% | 15 years | Monthly | ≈ ₹50,45,000 | ≈ ₹32,45,000 |
The SIP example shows the same principle: regular investing plus compounding can build a large corpus even if each instalment is modest. Use the SIP Calculator for a detailed month-by-month projection.
How to read the result
- Maturity value — the total amount you receive if you stay invested for the full tenure and the rate does not change.
- Total interest — the gain from compounding. It is not the same as the annual interest multiplied by the number of years.
- Principal share — in long tenures, the interest component often exceeds the principal. That is normal.
- Effective annual rate — use this to compare products with different compounding frequencies.
- Year-wise table — shows how the interest earned each year starts small and grows. This is the power of compounding in action.
- Post-tax value — most calculators show pre-tax figures. Interest on fixed deposits is taxable at your slab rate. Deduct tax to get the in-hand amount.
Rule of 72
The Rule of 72 is a quick way to estimate how long an investment takes to double. Divide 72 by the annual rate of return. At 8%, money doubles in roughly 72 ÷ 8 = 9 years. At 12%, it doubles in about 6 years. At 6%, it takes about 12 years.
This rule assumes yearly compounding and a constant rate. It is an approximation, but it is useful for quick mental maths. For exact figures, use the calculator.
Compounding and inflation
Compounding works both ways. Inflation compounds too, which means the cost of living rises exponentially over time. A 6% inflation rate halves the purchasing power of money in about 12 years. That is why an investment that only matches inflation does not build real wealth.
Your real return is the nominal return minus inflation. If a fixed deposit gives 7% and inflation is 6%, the real return is about 1%. Over 20 years, that barely grows your purchasing power. Use the Inflation Calculator to see how prices may change, and the Retirement Planning Calculator to plan a corpus that keeps pace.
Common mistakes to avoid
- Ignoring compounding frequency. Two deposits with the same headline rate can give different returns if one compounds quarterly and the other yearly.
- Using an unrealistic rate. Equity returns are not fixed. Test a lower rate as well as a higher one.
- Forgetting tax. Interest on fixed deposits is added to your income and taxed at your slab rate. TDS may apply if interest exceeds the threshold.
- Stopping early. The last few years of a long tenure contribute the largest absolute gains. Premature withdrawal can cut the maturity value sharply.
- Comparing a compounded product with a simple-interest product on headline rate alone. Compare effective annual yield.
- Not accounting for inflation. A large nominal corpus may not be enough in real terms after 20 years.
- Assuming the calculator includes fees or expense ratios. Mutual fund returns are shown net of expenses, but other products may have charges not reflected here.
Frequently asked questions
What is the difference between compound interest and simple interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus the interest already earned. Over long periods, compound interest produces much higher maturity values.
Which compounding frequency is best for me?
More frequent compounding gives a slightly higher effective yield for the same headline rate. But the difference is small. The bigger factors are the rate, the tenure and whether you keep reinvesting. Choose a product that matches your liquidity needs and tax situation.
Does this calculator work for SIPs?
Many compound interest calculators have an SIP mode where you enter a monthly contribution. If yours does not, use the SIP Calculator. The underlying maths is the same: each instalment compounds for the remaining period.
Is the maturity value guaranteed?
Only for fixed deposits and small savings schemes where the rate is contracted. For market-linked investments such as mutual funds, the value can go up or down. The calculator assumes a constant rate for illustration.
How is interest on fixed deposits taxed?
Interest is added to your total income and taxed at your slab rate. Banks deduct TDS if interest exceeds the notified threshold in a financial year. Senior citizens have a higher TDS threshold and a deduction under Section 80TTB. Use the Income Tax Calculator to estimate your liability.
Can I use this for PPF or EPF?
Yes. PPF and EPF have a notified rate that is compounded yearly. Enter the rate, the yearly contribution and the tenure. The PPF Calculator is built specifically for that scheme and handles the 15-year lock-in and extension rules.
What rate should I assume for equity mutual funds?
There is no guaranteed rate. Many planners use 10–12% for long-term equity, but actual returns vary widely. Run the calculator at 8%, 10% and 12% to see a range of outcomes. Do not plan on the highest number alone.
Why is the interest in later years so much larger?
Because the base on which interest is calculated has grown. Each year’s interest is added to the principal, so the next year earns interest on a larger amount. This is the compounding effect.
Does the calculator account for inflation?
No. It shows nominal values. To see real purchasing power, subtract inflation from the return or use the Inflation Calculator.
Related calculators
Related guides
Checklist for compound interest planning
- Tenure and rate tested together — not just the headline rate
- Compounding frequency checked for the product you are comparing
- Tax on interest estimated before you finalise the plan
- Inflation-adjusted real return calculated for long goals
- Emergency fund kept separate from long-term investments
- Regular contributions increased each year where possible
- Premature withdrawal penalties and lock-in periods read
- Projection reviewed at least once a year
Disclaimer: This compound interest calculator and the content on this page are for education and mathematical estimation only. They are not investment advice, a guarantee of returns, or a substitute for professional consultation. Market-linked investments carry risk, and fixed-deposit rates change on renewal. Tax treatment depends on your income slab and the current provisions of the Income-tax Act. Results depend entirely on the inputs you enter. Verify all rates, fees and tax rules with the product provider or a qualified adviser before you invest. Harshonomics is not a lender, a mutual fund distributor, or a SEBI-registered Investment Adviser.