Compound Interest Calculator
Model compound growth with lump sums, recurring contributions, timing options, continuous compounding, goal solvers, and full schedules.
Compound Growth, Contributions & Solver Toolkit
Calculate future value, total interest, required return, and full growth schedules with flexible compounding and deposit timing.
Understand compounding, contributions, and growth assumptions
Compound interest is interest calculated on an amount that already includes interest earned in earlier periods. For a principal P, annual nominal rate r, m compounding periods per year, and time t in years, the basic no-contribution formula is A = P × (1 + r/m)^(m×t). This formula assumes the quoted rate stays constant, interest is credited as specified, and no fees or withdrawals change the balance. Regular contributions need an additional series of cash flows and depend on when deposits arrive.
For example, a deposit of $1,000 at a 6% nominal annual rate compounded monthly for one year is about $1,061.68 before taxes and fees. The return differs from simply applying 6% to the starting amount because each month’s interest increases the base for the next month. A calculator that accepts monthly contributions may assume deposits occur at the beginning or end of each month; that timing changes the result, particularly over long periods.
A projected balance is not a guarantee of returns. Investment returns fluctuate, bank products can change rates, and inflation reduces purchasing power even when the account grows in nominal dollars. Compare the input rate with the product’s terms, review whether taxes or fees are omitted, and consider a range of conservative assumptions rather than relying on one precise future figure.