Compound interest and savings calculator

What this tool does

It shows what a starting amount and regular deposits become when the interest they earn also earns interest. Enter what you have today, what you add each month or year, the yearly rate, how often the interest is added and for how many years. You get the final balance, how much of it you paid in, how much is interest, a chart, and a table with one row per year that you can copy or download as CSV. Add an inflation rate and it also shows the balance in today's money. Everything is calculated in your browser.

How to use it

1. Type the starting amount and the regular contribution (either may be empty, but not both) and choose whether you add it every month or every year, at the start or at the end.
2. Enter the interest rate per year, choose how often interest is added (daily, weekly, monthly, quarterly, every six months or yearly) and the number of years, from 1 to 100.
3. Optionally enter the yearly inflation to see the balance in today's money, and pick a currency so amounts show with the right symbol and number of decimals. A number written like 1.234,56 is understood too, and the page tells you how it read it.

How the interest is calculated

The rules are fixed and stated here so the numbers can be checked. The year is split into equal compounding periods, and at the end of each one the interest on the balance is added. There is no rounding between periods: the balance is carried with at least thirty more digits than a cent and rounded half up to the cent once, when it is shown. So 10,000 at 5% compounded monthly for 10 years is exactly the textbook 10,000 × (1 + 0.05 ÷ 12)^120, which is 16,470.09. Money you deposit part-way through a compounding period earns simple interest for the time it was in the account, so a deposit at the end of a period joins after that period's interest and one at the start earns the whole period. The interest in the table is the balance minus everything you have paid in, so each row adds up. In today's money means the balance divided by (1 + inflation) for each year that has passed.

Worked examples

• How often interest is added. 10,000 at 5% for 10 years ends at 16,288.95 compounded yearly, 16,386.16 every six months, 16,436.19 quarterly, 16,470.09 monthly, 16,483.25 weekly and 16,486.65 daily. The gain flattens quickly: even interest added every instant would only reach 16,487.21.
• Regular saving. 500 a month at the end of each month at 7% compounded monthly for 30 years grows to 609,985.50, of which you paid in 180,000.
• Start or end of the month. Depositing 1,000 a month at 12% for one year gives 12,809.33 when you deposit at the start of each month and 12,682.50 at the end.
• Inflation. 10,000 at 7% for 10 years becomes 20,096.61, but with 3% yearly inflation that is worth 14,953.77 in today's money.

Good to know

This is an illustration, not financial advice. It does not include taxes, fees, a rate that changes over time, contributions that grow with your income or irregular withdrawals, and real investments can lose value, which a fixed rate cannot show. If you want to borrow rather than save, the loan calculator gives the schedule for a loan. To work out a percentage change or an increase, use the percentage calculator, and the number to words converter writes an amount out in words.