Savings Calculator

This calculator answers the question every saver eventually asks: if I keep this up, what will I actually have? It takes three habits — a starting deposit, a monthly contribution, and the APY your account pays — and projects the balance month by month, splitting the final number into what you deposited and what interest added on top.

The split matters more than the total. Early on, nearly all of the balance is your own contributions; interest looks like a rounding error. Stretch the horizon and the interest share grows steadily, because each month's interest starts earning interest of its own. Watching that share climb is the clearest argument for starting early and for refusing to leave money at a near-zero rate.

The projection runs your balance one month at a time. Each month, the balance grows by the monthly equivalent of your APY, then your contribution lands on top. The loop repeats for the full horizon, recording the balance along the way — that recorded path is the chart you see.

Because APY is already an effective annual figure, the calculator converts it to a true monthly rate — (1 + APY)^(1/12) − 1 — rather than naively dividing by 12. The difference is small at savings rates but it keeps the annual growth exactly equal to the APY the bank advertises.

Each month: balance = balance × (1 + i) + contribution, where i = (1 + APY)^(1/12) − 1. Interest earned is simply the final balance minus everything you put in (starting deposit plus all contributions). The starting deposit alone follows FV = P × (1 + APY)^years — the contribution stream is what the month-by-month loop adds on top of that.

Assumptions worth knowing: the APY is treated as constant for the whole horizon, though real savings rates float with the Fed; contributions land at the end of each month and never skip; and the result is pre-tax and ignores inflation, so a 10-year figure buys less in 10-years' dollars than it suggests. Treat long horizons as a trajectory, not a promise.

The number to judge isn't the future balance — it's the APY driving it. High-yield savings accounts have recently paid roughly 4–4.5% APY, while the standard rate at the biggest branch banks sits near 0.05%. On this example's balances, that gap is the difference between roughly $1,900 of interest over five years and about $20. Same deposits, same discipline — nearly a hundred times the payout.

If your projected interest looks thin, check the rate before questioning the habit: moving to a high-yield account is a one-time, ten-minute fix that repriced every future dollar. If the rate is already competitive and the balance still disappoints, the horizon or the contribution is the lever — at savings-account rates, how much and how long you save matters far more than squeezing another tenth of a percent of yield.