Compound interest calculator

Enter your starting balance, monthly contribution and interest rate to see your final balance, the interest earned and year-by-year growth instantly. Works for savings, deposits and investment projections in any currency.

%
% per year
years

Result

Final balance
68,229.96
Total contributions (incl. initial deposit)
34,000.00
Total interest earned
34,229.96
Effective annual rate (APY / AER)
5.12%
Growth year by year
YearContributionsInterestBalance at year end
11,200.00539.5111,739.51
21,200.00628.4913,568.00
31,200.00722.0615,490.06
41,200.00820.4017,510.46
51,200.00923.7419,634.20
61,200.001,032.4221,866.62
71,200.001,146.6524,213.27
81,200.001,266.6926,679.96
91,200.001,392.8929,272.85
101,200.001,525.5431,998.39
111,200.001,665.0034,863.39
121,200.001,811.5737,874.96
131,200.001,965.6641,040.62
141,200.002,127.6244,368.24
151,200.002,297.8447,866.08
161,200.002,476.8151,542.89
171,200.002,664.9055,407.79
181,200.002,862.6559,470.44
191,200.003,070.5263,740.96
201,200.003,289.0068,229.96

How it is calculated

How compound interest works

Compound interest means you earn interest on your interest: once interest is credited, it earns interest itself in the following periods. Growth is therefore not linear but exponential – the longer the money stays invested, the faster it grows.

Compound interest formula

Single deposit: A = P × (1 + r/n)n·t, with principal P, annual rate r, n compounding periods per year and t years. Example: 10,000 at 5% for 10 years grows to 16,288.95 with annual compounding.

With monthly contributions (monthly compounding, deposits at month end): A = P × (1 + i)N + C × ((1 + i)N − 1) ÷ i, with i = r ÷ 12, N = 12 × t and monthly contribution C. Example: 500 a month at 7% for 30 years grows to about 609,985 – you paid in 180,000, the other 429,985 or so is interest.

In Excel or Google Sheets: =FV(5%/12, 12*20, -100, -10000) gives the balance of 10,000 plus 100 a month at 5% compounded monthly over 20 years: 68,229.77. The calculator shows 68,229.96 because it rounds each interest credit to the cent.

Rule of 72: divide 72 by the interest rate to estimate how many years it takes to double your money – 72 ÷ 5 = 14.4 years; the exact value is ln(2) ÷ ln(1.05) = 14.2 years with annual compounding.

Daily, monthly or annual compounding

The more often interest is credited, the higher the effective annual rate (APY in the US, AER in the UK). 10,000 at 5% for 10 years grows to:

CompoundingFinal balanceEffective annual rate
annually16,288.955.00%
quarterly16,436.195.09%
monthly16,470.095.12%
daily (365)16,486.655.13%
continuously (P × ert)16,487.215.13%

The step from monthly to daily compounding adds very little. This calculator compounds monthly at most; for daily or continuous compounding use the formulas above.

Monthly contributions: each deposit earns simple interest until the next compounding date and is compounded from then on – the way banks calculate savings plans. The yearly increase raises the contribution by the given percentage from the second year on, for example to keep pace with pay rises.

Adjusting for inflation

To see the final balance in today's money, divide it by (1 + inflation rate)years. The 609,985.57 from 500 a month at 7% over 30 years is worth about 251,306 in today's money at 3% inflation. You can also enter the real rate (1.07 ÷ 1.03) − 1 = 3.88% instead of 7%; this assumes contributions that rise with inflation. Simply subtracting inflation from the rate (4%) is only a rough shortcut.

What the calculator does not include

The result is before tax, fees and inflation, with a fixed interest rate and no withdrawals – it models the saving phase only, not a withdrawal or retirement income plan. Interest on savings may be taxable depending on where you live and on accounts such as a 401(k), IRA, ISA or PPF. Investment returns are not fixed; for stocks or funds, an assumed average return only gives a rough projection.

Frequently asked questions

How do you calculate compound interest?

Final balance = principal × (1 + rate ÷ n)n × years, where n is the number of compounding periods per year. 10,000 at 3% compounded annually for 20 years becomes 18,061.11. Regular contributions add their own compounded amounts on top.

How do I calculate compound interest with monthly contributions?

Add the compounded principal and the future value of the contributions: C × ((1 + i)N − 1) ÷ i with i = annual rate ÷ 12 and N = number of months. 500 a month at 7% for 30 years grows to about 609,985. The calculator does this for you, including a yearly increase.

Is monthly compounding better than annual compounding?

Yes, at the same nominal rate. 5% compounded monthly equals an effective annual rate of 5.12%, because interest credited earlier in the year earns interest itself.

Can I use this as a daily compound interest calculator?

The calculator compounds up to monthly. Daily compounding gives almost the same result: 10,000 at 5% for 10 years is 16,470.09 with monthly and 16,486.65 with daily compounding – a difference of 0.1%.

How long does it take to double my money?

Years = ln(2) ÷ ln(1 + rate). At 5% that is 14.2 years, at 7% 10.2 years. The rule of 72 (72 ÷ rate) gives a quick estimate.

Does it work in pounds, dollars or rupees?

Yes. Compound interest does not depend on the currency – enter the amounts in your currency and read the results in the same unit.

Are taxes and inflation included?

No. The figures are before tax and inflation. For today's money, divide the result by (1 + inflation)years: 609,985.57 after 30 years is about 251,306 at 3% inflation. Whether and how interest is taxed depends on your country and on the type of account.

Sources and legal basis

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