Add a lump sum, a monthly contribution, or both — see your future value, required principal, or time to reach a goal, with a year-by-year growth breakdown. Interest compounds monthly.
Quick answers to the questions people ask most about compound interest.
Each month, interest is added to the current balance, then the contribution is added on top, and this repeats for every month of the term. Because contributions keep adding to the base that earns interest, the balance grows faster than a lump sum alone.
Simple interest is calculated only on the original principal each year. Compound interest is calculated on the principal plus all interest earned so far, so growth accelerates over time rather than staying flat.
Work out the future value your monthly contributions alone will reach, subtract that from your target, then divide the remainder by the growth multiplier for your term. This calculator does that automatically once you enter your contribution, rate, and years.
This calculator simulates your balance month by month — adding interest, then your contribution, then repeating — until it reaches your target, and reports how many years that takes.