All Digi HubCompound interest calculator
Money that earns interest on its interest grows faster each year. Enter a starting amount, a monthly addition, a rate and the compounding frequency to see the final value, interest earned and a year-by-year table. The calculator is free, needs no sign-up, is for learning and planning only, and your numbers stay on your device.
How it works
Without additions, compound interest follows A = P × (1 + r ÷ n)^(n × t), where r is the yearly rate, n the times compounded a year and t the years. Because this tool also adds money monthly, it converts the rate to an equivalent monthly rate: monthly rate = (1 + r ÷ n)^(n ÷ 12) − 1.
Each month, balance = balance × (1 + monthly rate) + monthly addition, so additions go in at the end of the month. Interest earned = final value − everything you put in. The time to double uses the rule of 72: years ≈ 72 ÷ rate. This calculator is for learning and planning only, not investment advice.
How to use it
- Enter the starting amount and how much you add every month.
- Enter the yearly interest rate and number of years.
- Choose yearly, half-yearly, quarterly or monthly compounding.
Questions
What is the formula for compound interest?
A = P × (1 + r ÷ n)^(n × t). P is the starting amount, r the yearly rate as a decimal, n the number of times interest is added each year and t the number of years. The calculator also handles regular monthly additions.
Does monthly compounding make a big difference?
It helps a little compared with yearly compounding at the same rate. Regular additions and more years usually make a much bigger difference to the final amount. Switch the compounding option in the calculator to compare.
What is the rule of 72?
Divide 72 by the yearly interest rate to estimate how many years money takes to double. At 8%, it is about 9 years. It is an approximation that works best for rates between about 6% and 10%.
Is this free and is it investment advice?
Yes, it is free, needs no sign-up, and your numbers stay on your device unless you choose to send them. It is for learning and planning only, not investment advice, and returns are never guaranteed.
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