Compound Interest Calculator

See how a balance grows with compound interest and regular contributions — with the final balance, how much is interest, and a year-by-year breakdown.

Final balance —
Total contributions — paid in
Total interest — earned

How Compound Interest Works

Interest that earns interest, plus whatever you add along the way.

1

Set the starting point

Enter your starting amount, the annual interest rate, and how often interest compounds — daily, monthly, quarterly or yearly. More frequent compounding earns a little more.

2

Add contributions and time

Choose how much you add each month or year and whether it lands at the start or end of the period, then set how many years to run. Every deposit compounds from the day it is added.

3

See growth vs deposits

The result splits your final balance into what you paid in and what interest added, with a year-by-year table. As a rough check, the Rule of 72 estimates doubling time: 72 ÷ rate. Working out loan repayments instead? Try the Loan Calculator.

Frequently Asked Questions

What is the compound interest formula?
The core formula is A = P(1 + r/n)nt, where P is the starting principal, r is the annual interest rate as a decimal, n is how many times a year interest compounds, and t is the number of years. For example, 10,000 at 5% compounded monthly for 10 years is 10,000 × (1 + 0.05/12)12×10, which is about 16,470. When you add regular contributions the calculator also sums the growth of each deposit, so the year-by-year table reflects both the principal and everything you paid in.
How does compounding frequency affect returns?
The more often interest compounds, the more you earn, because each block of interest starts earning its own interest sooner. The effect is real but modest: 10,000 at 5% for a year is 500 with annual compounding, about 511.62 with monthly, and about 512.67 with daily. The gap between monthly and daily is only a few dollars, while the gap between annual and monthly is larger. This calculator lets you switch between daily, monthly, quarterly and annual compounding to compare them directly.
How do regular contributions change the total?
Regular contributions usually matter more than the starting amount over a long period, because every deposit compounds from the day it is added. Adding 100 a month to a 10,000 balance at 5% for 10 years pushes the final balance well above what the principal alone would reach, and most of the extra is money you paid in rather than interest. The calculator separates total contributions from total interest so you can see how much of the final figure is growth and how much is your own deposits.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long an amount takes to double: divide 72 by the annual interest rate. At 6%, money doubles in roughly 72 ÷ 6 = 12 years; at 8%, in about 9 years. It is an approximation that works best for rates between about 5% and 10%, and it assumes interest compounds without withdrawals. Use it for a rough mental check, then use this calculator for the exact figure, since it accounts for your compounding frequency and any contributions.