Compound Interest Calculator
Calculate compound interest growth with regular monthly contributions. Compare balance with and without contributions.
How to use this calculator
👉 Fill in the boxes below and your answer appears instantly — no maths needed, we do it all for you! 🎉
In plain English — what does this do?
🌱 When you save money in a bank, the bank gives you a small gift (called interest) for keeping it there. Then next year, you get a gift on your gift too! This tool shows how much your money will grow over time.
A compound interest calculator shows how an investment grows when interest is earned not just on your principal but also on previously accumulated interest. Adding regular monthly contributions dramatically accelerates growth — this calculator shows both the balance from principal alone and the balance including contributions so you can see the real impact of consistent investing. The Rule of 72 gives a quick mental shortcut: divide 72 by your annual rate to find approximately how many years it takes to double your money.
How much money are you starting with?
The % bonus the bank gives you each year
How long will the money stay invested?
Leave at 0 if you're not adding money monthly
Your money grows to 🌱
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Without monthly adds
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Total you put in
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Free interest earned 🎉
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Money grew by
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⚡ Fun fact — Rule of 72
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What is Compound Interest Calculator?
A compound interest calculator shows how an investment grows when interest is earned not just on your principal but also on previously accumulated interest. Adding regular monthly contributions dramatically accelerates growth — this calculator shows both the balance from principal alone and the balance including contributions so you can see the real impact of consistent investing. The Rule of 72 gives a quick mental shortcut: divide 72 by your annual rate to find approximately how many years it takes to double your money.
How to use it
- 1️⃣ Enter your initial investment (principal).
- 2️⃣ Input the annual interest rate.
- 3️⃣ Enter the number of years.
- 4️⃣ Select how often interest compounds.
- 5️⃣ Optionally add a monthly contribution amount.
- 6️⃣ Review future value with and without contributions, total interest, and growth percentage.
Formula & Variables
Variable Definitions:
💡 See it in action — a real example
📊 Compounding Frequency Comparison ($10,000 at 7% over 20 Years)
Comparing the effect of different compounding periods on identical principal and interest rates.
| Compounding Frequency | Annual Compounding Cycles (n) | Final Balance (A) | Total Interest Earned | Effective Annual Yield (APY) |
|---|---|---|---|---|
| Annually | n = 1 | $38,696.84 | $28,696.84 | 7.000% |
| Semi-Annually | n = 2 | $39,592.60 | $29,592.60 | 7.123% |
| Quarterly | n = 4 | $40,063.89 | $30,063.89 | 7.186% |
| Monthly | n = 12 | $40,387.39 | $30,387.39 | 7.229% |
| Daily | n = 365 | $40,546.54 | $30,546.54 | 7.250% |
| Continuously | n → ∞ | $40,552.00 | $30,552.00 | 7.251% |
* More frequent compounding increases yield, but gains taper off asymptotically beyond daily compounding.
📊 The Power of Time: $10,000 + $200/Month at 7% Annual Return
Growth trajectory illustrating how compound interest dominates contributions over multi-decade spans.
| Investment Horizon | Total Money Deposited | Total Compound Interest Earned | Total Portfolio Balance | % of Wealth from Interest |
|---|---|---|---|---|
| 5 Years | $22,000 | $4,874 | $26,874 | 18.1% |
| 10 Years | $34,000 | $18,348 | $52,348 | 35.1% |
| 15 Years | $46,000 | $44,984 | $90,984 | 49.4% |
| 20 Years | $58,000 | $90,239 | $148,239 | 60.9% |
| 25 Years | $70,000 | $161,281 | $231,281 | 69.7% |
| 30 Years | $82,000 | $269,726 | $351,726 | 76.7% |
* By year 30, over 76% of the portfolio's total value is pure compound interest created out of nothing.
❓ Common questions
- What is the Rule of 72?
- Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7%, money doubles in roughly 72/7 = 10.3 years. At 10%, it doubles in about 7.2 years. It works best for rates between 2% and 20%.
- What is the difference between simple and compound interest?
- Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus all previously earned interest, leading to exponential rather than linear growth. The difference is small over short periods but enormous over decades.
- How often should interest compound for maximum growth?
- More frequent compounding produces slightly higher returns. Daily compounding yields marginally more than monthly, which yields more than annual. The difference is significant mainly at very high rates or very long time horizons.
- What is continuous compounding?
- Continuous compounding is the mathematical limit as compounding frequency approaches infinity: A = P × e^(r×t). At 7% for 10 years, continuous compounding gives $20,138 vs. $20,097 for daily compounding — the difference is minimal in practice.
- What annual return should I use for stock market investments?
- The long-run average annual return of broad stock market indices like the S&P 500 is roughly 7–10% before inflation (about 5–7% after inflation). Use a conservative 6–7% for long-term planning to account for market variability and sequence-of-returns risk.
- Does compound interest work against me on debt?
- Yes. On credit cards and loans, compound interest works against you — unpaid balances grow rapidly. This is why paying off high-interest debt quickly is mathematically equivalent to earning that same interest rate as a guaranteed investment return.