Compound interest calculator
See how your savings grow over time with interest on top of interest and regular deposits.
- Final balance
- 109,333.14
- Total deposits
- 58,000.00
- Interest earned
- 51,333.14
For guidance only, not financial advice. Real offers depend on fees, taxes and terms. Check the exact figures with your bank, lender or accountant before you decide.
Growth by year
| Year | Chart | Deposits | Interest | Balance |
|---|---|---|---|---|
| 1 | 12,400.00 | 567.39 | 12,967.39 | |
| 2 | 14,800.00 | 1,286.60 | 16,086.60 | |
| 3 | 17,200.00 | 2,165.39 | 19,365.39 | |
| 4 | 19,600.00 | 3,211.93 | 22,811.93 | |
| 5 | 22,000.00 | 4,434.80 | 26,434.80 | |
| 6 | 24,400.00 | 5,843.03 | 30,243.03 | |
| 7 | 26,800.00 | 7,446.09 | 34,246.09 | |
| 8 | 29,200.00 | 9,253.96 | 38,453.96 | |
| 9 | 31,600.00 | 11,277.11 | 42,877.11 | |
| 10 | 34,000.00 | 13,526.55 | 47,526.55 | |
| 11 | 36,400.00 | 16,013.87 | 52,413.87 | |
| 12 | 38,800.00 | 18,751.23 | 57,551.23 | |
| 13 | 41,200.00 | 21,751.44 | 62,951.44 | |
| 14 | 43,600.00 | 25,027.92 | 68,627.92 | |
| 15 | 46,000.00 | 28,594.83 | 74,594.83 | |
| 16 | 48,400.00 | 32,467.01 | 80,867.01 | |
| 17 | 50,800.00 | 36,660.09 | 87,460.09 | |
| 18 | 53,200.00 | 41,190.49 | 94,390.49 | |
| 19 | 55,600.00 | 46,075.46 | 101,675.46 | |
| 20 | 58,000.00 | 51,333.14 | 109,333.14 |
Your depositsInterest earned
How it works
The math of compound interest
For a single amount, the classic formula is:
A = P × (1 + r ÷ n)^(n × t)
where P is the starting amount, r the yearly rate as a decimal, n how many times a year interest is added and t the number of years. MathyBit works month by month so it can add your deposits along the way.
Example: 10,000 at 5% compounded yearly grows to 10,000 × 1.05²⁰ ≈ 26,533 in 20 years. The interest alone, about 16,533, is more than the starting amount, and that's without adding anything.
Why starting early matters
Because growth builds on itself, time can do more work than the amount you put in. At a 7% yearly return, someone who saves 200 a month from age 25 to 35 and then stops ends up with about 281,000 at 65, while someone who saves 200 a month from 35 to 65 ends up with about 244,000, despite depositing three times as much. At lower rates the gap closes, so try your own numbers.
Borrowing rather than saving? Interest works against you then; see how much with the loan calculator.
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Frequently asked questions
What is compound interest?
Interest earned on both your deposits and the interest you have already earned. Each year's interest is added to the balance, so next year it earns interest too. Over long periods this snowball effect becomes the biggest part of the growth.
What is the rule of 72?
A quick way to estimate how long it takes to double your money: divide 72 by the yearly interest rate. At 6%, money doubles in about 72 ÷ 6 = 12 years.
Does compounding frequency matter much?
A little. The more often interest is added, the slightly faster the growth: 5% compounded monthly works out to about 5.12% a year. The rate and the number of years matter far more.
Should I use this for investments?
It is a useful way to picture growth, but investment returns go up and down and are never guaranteed. The calculator also ignores taxes, fees and inflation. Treat the result as an illustration, not a forecast or advice.
When are the monthly deposits added?
At the end of each month. The starting amount is invested from day one, and interest is compounded at the frequency you choose.