Compound Interest Calculator

Compound interest is interest earned on both your original balance and on the interest it's already earned, so the growth accelerates over time rather than staying flat. The formula for a single lump sum is A = P(1 + r/n)^(nt), where P is the starting amount, r is the annual rate, n is how many times a year interest compounds, and t is the number of years.

Why compounding frequency matters less than you'd think

Moving from annual to daily compounding at the same stated rate makes a small difference, not a dramatic one. The two things that actually move the final number are the rate itself and how long the money stays invested - which is why starting early tends to matter more than chasing a slightly better compounding schedule.

A reminder on regular contributions

Adding even a modest regular contribution on top of a lump sum can meaningfully change the outcome over a long time horizon, because each contribution gets its own runway to compound. This calculator accounts for that properly - each contribution grows for the time it's actually been in the account, rather than being added on at the end.