Compound Interest Calculator
See what a starting amount grows into once each round of interest is added back and starts earning interest of its own. Set the annual rate, the term in years and how often interest compounds — yearly, half-yearly, quarterly, monthly or daily — and add a regular monthly contribution if you make one. The result separates what you put in from what the interest added.
This is an illustration, not a promise. It assumes the rate you enter stays the same for the whole term, which real savings and investment rates rarely do. Monthly contributions are treated as paid at the end of each month and grown at the monthly equivalent of the frequency you picked, so both parts of the balance earn the same effective annual return; the number of contributions is the term rounded to the nearest whole month. Tax, fees and inflation are not included, and this is not financial advice. Amounts work in any currency.
How to calculate compound interest
- Enter the starting amount and the annual interest rate.
- Enter the term in years and pick how often interest compounds.
- Add a monthly contribution if you make one, then read the final amount, the total contributed and the interest earned.
When you'd use this
- Planning a savings goal — Checking whether a deposit and a monthly habit will reach a target amount by a chosen date.
- Comparing two accounts — Putting a slightly higher rate against a more frequent compounding schedule to see which actually pays more.
- Understanding a quoted return — Turning an annual percentage into a figure you can picture at the end of the term.
- Checking a statement — Seeing whether the balance an account reports is roughly what the stated rate and term should produce.
Good to know
- Frequency changes the answer — At the same headline rate, interest added more often earns interest sooner. Over ten years at 5%, a lump sum grows a little more with daily compounding than with yearly — the gap is real but usually smaller than people expect.
- Contributions are added at month end — Each monthly contribution starts earning from the end of the month it is paid, so the final one earns nothing. If your bank credits deposits at the start of the month, the true balance will be slightly higher than shown.
- Contributions follow the frequency you pick — The monthly stream is grown at the monthly equivalent of the compounding rate you selected, so both the starting amount and the contributions earn the same effective annual return. The number of contributions is the term rounded to the nearest whole month.
- Tax, fees and inflation are left out — The figure is a gross balance. Interest is taxable in most places, account fees reduce it further, and inflation reduces what the final amount will buy. A fixed rate for the whole term is an assumption, not a forecast.
Frequently asked questions
What formula does this use?
For the starting amount it is the standard compound interest formula, A = P × (1 + r/(100n))^(n×t), where P is the amount, r the annual rate, n the compounding periods per year and t the years. Monthly contributions are added as an ordinary annuity on top.
How are the monthly contributions treated?
Each one is assumed to be paid at the end of its month and then to grow at the monthly equivalent of the compounding rate you chose — that is (1 + r/(100n))^(n/12) − 1. This keeps both parts of the balance earning the same effective annual return.
Why does daily compounding barely beat yearly?
Because the extra benefit comes only from interest earning interest a little sooner. At 5% for ten years the difference on a starting amount of 1,000 is under 20 in whatever currency you use, so the headline rate matters far more than the frequency.
Can I use it for a loan or a credit card?
Only as a rough illustration of a balance left untouched. It has no repayments, so it will not tell you what a loan costs — use the EMI Calculator for a loan with regular repayments.
Does it show the amount before or after tax?
Before tax. Interest is treated as income in most tax systems and some accounts deduct tax at source, so the amount that actually reaches you is usually lower than the figure shown here.