Compound Interest Calculator
The Compound Interest Calculator shows how your money grows when interest is earned on both the principal and previously earned interest.
Compound Interest Calculator
The initial amount you invest or save.
The annual interest rate.
How long the money grows.
What the result means
The future value includes your original principal plus all interest earned. More frequent compounding results in slightly higher returns because interest is calculated on a larger balance more often.
How to use this calculator
- 1Enter your initial principal amount.
- 2Enter the annual interest rate.
- 3Enter the time period in years.
- 4Select how often interest is compounded.
- 5Press Calculate to see your future value.
The formula
The calculation uses a standard, verifiable formula. Here it is in its simplest form.
What each variable means
| Symbol | Name | Description |
|---|---|---|
| P | Principal | The initial amount invested. |
| r | Rate | Annual interest rate as a decimal. |
| n | Compounds | How many times interest compounds per year. |
| t | Time | Investment period in years. |
Step-by-step example
Example: ₹1,00,000 at 8% for 5 years (monthly compounding)
- 1Monthly rate = 8% / 12 = 0.6667% = 0.006667
- 2Periods = 12 × 5 = 60
- 3A = 1,00,000 × (1.006667)⁶⁰
- 4(1.006667)⁶⁰ ≈ 1.4898
- 5A ≈ ₹1,48,984
- 6Interest = ₹1,48,984 − ₹1,00,000 = ₹48,984
Result
Future value ≈ ₹1,48,984
What changes the result
- Higher principal amounts grow proportionally.
- Higher interest rates dramatically increase growth.
- Longer time periods allow more compounding cycles.
- More frequent compounding yields slightly higher returns.
Edge cases to be aware of
Unusual situations handled correctly
- Simple interest (compounds = 1) gives the lowest growth.
- Daily compounding gives the highest growth among common frequencies.
- Zero interest means no growth.
Common mistakes
Avoid these errors
- Using the annual rate without dividing by compounding periods.
- Forgetting that compound interest grows exponentially, not linearly.
- Confusing simple and compound interest.
Assumptions
- Interest rate remains constant.
- No additional deposits or withdrawals.
- Interest is reinvested (not withdrawn).
Limitations
- Actual returns may vary, especially for market-linked investments.
- Does not account for taxes on interest earned.
- Inflation reduces the real value of future money.
Key terms to know
Principal+
Compound interest+
Compounding frequency+
Future value+
Nominal rate+
Effective annual rate+
Rule of 72+
Real-world scenarios
The power of time
Two people each invest ₹1,00,000 at 8% — one for 10 years, the other for 20 years.
What it means: The 10-year investment grows to about ₹2,21,964, while the 20-year investment grows to about ₹4,92,680. Doubling the time more than doubles the result because compounding is exponential, not linear.
Compounding frequency matters
₹1,00,000 at 8% for 10 years, compounded annually vs monthly.
What it means: Annual compounding gives about ₹2,15,892; monthly compounding gives about ₹2,21,964. The difference is modest over 10 years but grows with larger amounts and longer periods.
Rate sensitivity
₹1,00,000 over 20 years at 6% vs 10%.
What it means: At 6% the result is about ₹3,20,714; at 10% it is about ₹6,72,750. A 4 percentage-point rate difference more than doubles the outcome over 20 years — a powerful illustration of rate sensitivity.
Inflation erodes real growth
An investment grows at 8% while inflation runs at 5%.
What it means: The nominal value grows, but the real (inflation-adjusted) growth is roughly 3% per year. Understanding the difference between nominal and real returns is essential for long-term planning.
Related concepts
Simple interest
Simple interest is calculated only on the original principal, so it grows linearly. Compound interest grows exponentially because interest earns interest.
Systematic investment plans (SIP)
A SIP adds regular contributions on top of compounding, which can dramatically accelerate growth compared to a one-time investment.
Fixed deposits
Fixed deposits typically compound interest at a set frequency. Comparing compounding options helps you choose the best return.
Inflation and purchasing power
Inflation reduces what your future money can buy. Adjusting compound-growth projections for inflation gives a more realistic picture of real wealth.