What this savings calculator does
The savings calculator projects what an initial deposit plus regular monthly contributions will grow to at a given interest rate. Use it for high-yield savings, money market accounts, share savings or any account that pays a roughly steady rate. The result updates live, and the year-by-year table shows how the balance climbs over time — and how much of it is contributions versus interest.
How the math works
Two pieces, summed together:
- Initial deposit future value: P × (1 + r/12)12 × t
- Monthly deposits future value (ordinary annuity): PMT × [((1 + r/12)12 × t − 1) ÷ (r/12)]
where P is the initial deposit, PMT is the monthly contribution, r is the annual rate as a decimal, and t is years. The calculator compounds monthly, which is a close approximation of the daily compounding that real banks use — for savings rates the difference is pennies a year.
APR vs APY
Banks usually advertise APY (Annual Percentage Yield) for savings accounts. APY already includes the effect of compounding within the year, so a 5% APY account compounded monthly is paying about 4.89% nominal (APR). Most calculators (this one included) expect the input to be the headline rate that gets compounded. Using the APY directly is the simplest, most accurate approach — and that's exactly what the field is labelled.
Why even modest savings rates matter
Many Americans still keep "emergency" money in checking accounts paying 0.01%. A few minutes moving that money to a high-yield account at 4.5% makes a meaningful difference: $10,000 sitting in a 4.5% account for 5 years grows to about $12,517, earning $2,517 in interest while sitting there. At 0.01%, the same balance grows by about $5. The risk profile is identical — both are FDIC-insured deposit accounts — but the result is vastly different.
The compound advantage compounds
Look at the year-by-year table. Most of the interest in year 1 comes from the initial deposit, since contributions haven't had time to grow. By year 5, contributions plus their interest dominate. By year 10, the interest column alone is often larger than the original initial deposit. This is what people mean when they say "save early" — the same dollars contributed five years sooner are worth a lot more by the end.
What this calculator doesn't model
Interest rate changes (real high-yield savings rates move with the Fed funds rate), taxes (US savings interest is taxed as ordinary income each year), inflation (real purchasing power is lower over decades), and account fees (most online savings have none, but check). For inflation-adjusted projections, run the result through the inflation calculator. For variable-return investments, the investment calculator is more appropriate.