Compound interest calculator
Estimate a future amount from starting principal and monthly contributions. The model assumes each contribution is made at the end of the month.
Project compound growth
Calculation method
The starting principal grows as P × (1 + i)^n. Monthly contributions are assumed to be added at each month’s end and compound over the remaining periods. An effective annual rate is converted to an equivalent monthly rate using (1 + annual rate)^(1/12) − 1.
What this estimate leaves out
This is a mathematical projection, not a forecast or financial advice. It assumes a constant rate and excludes fees, taxes and inflation. Actual products may use different terms. No currency conversion is performed.
Frequently asked questions
Does this include inflation?
No. The result is nominal and does not adjust for changes in purchasing power.
Are monthly contributions made at the start or end of the month?
The model assumes contributions are made at the end of each month. Different timing changes the result.
How is the annual rate converted?
The entered annual rate is treated as an effective annual rate and converted geometrically to an equivalent monthly rate, rather than divided by 12.