Compound Interest Calculator
Project investment growth with recurring compounding. Your work stays on this device whenever possible.
How to use Compound Interest Calculator
- Enter the starting balance in Initial deposit ($) and a regular amount in Monthly contribution ($).
- Set Annual interest rate (%) and Investment period (years), which accepts whole years from 1 to 100.
- Choose Contribution timing: "End of month" or "Beginning of month", which makes each deposit earn one extra month of interest.
- Add an Estimated inflation rate (% optional) if you want a purchasing-power figure, then press "Calculate growth".
- Press "Download Annual Breakdown (CSV)" for a year-by-year table of starting balance, deposits, interest and ending balance.
Worked example
Enter Initial deposit 5,000, Monthly contribution 200, rate 6%, 20 years, End of month, inflation 2.5%. Each month the balance is multiplied by 1.005, then 200 is added. After 240 months the future value is 108,959.20 against 53,000.00 deposited, so interest is 55,959.20. Inflation-adjusted, 108,959.20 ÷ 1.025^20 gives 66,494.63.
When to use this tool
- Projecting a child's savings account with a regular monthly top-up.
- Showing the gap between early and late starts by running the same deposit for 20 and 30 years.
- Estimating what a lump sum would be worth in today's money after inflation.
Important limitations
A constant return ignores tax, fees, inflation, losses, and timing variation. Investment returns are not guaranteed.
Frequently asked questions
Does the Compounding frequency choice change the result?
In the current version the growth loop applies monthly compounding whichever option is selected, so switching to daily or annual leaves the figures unchanged. The selected label is only echoed at the bottom of the result.
What is the difference between the two timing options?
With deposits at the beginning of the month each contribution earns interest that same month, so the final balance is a little higher than with end-of-month deposits at the same rate.
What does the purchasing power line mean?
It divides the future balance by (1 + inflation) raised to the number of years. The result estimates what the money buys in today's terms, not a guaranteed return, and only appears when inflation is above zero.
Are taxes and fees included?
No. The projection assumes a constant rate with no fees, taxes or withdrawals, and interest is credited monthly. Real investments fluctuate, so treat the output as an illustration of compounding.
Can the period include partial years?
The field steps in whole years, and the schedule runs year by year. For a shorter horizon such as eight months, use the simple interest tool or an equivalent whole-year approximation.