Savings Growth Calculator

How does the compounding frequency change my balance?

Interest credited monthly compounds faster than the same rate credited annually, because each credit starts earning its own interest sooner. Over years the gap is real money, not rounding. Account terms specify the crediting schedule; when comparing two accounts with identical rates but different frequencies, the more frequent compounding wins by exactly the amount this calculator shows.

What does the calculation assume about my deposits?

The standard model treats deposits as end-of-period contributions; a deposit made at the start of each month earns one extra month of interest per deposit. Over a long horizon that timing choice shifts the outcome noticeably. Match the calculator's assumption to your actual habit, or run both and let the difference inform whether front-loading contributions is worth the strain.

APY versus the rate you were quoted

Two different numbers live on savings product pages, and entering the wrong one skews the result. APY includes the effect of compounding; the nominal annual rate does not. At a 5% nominal rate compounded monthly, the effective APY is (1 plus 0.05 divided by 12) to the 12th, minus 1, which lands near 5.12%. This calculator applies monthly compounding to the annual rate you type, which matches the behavior of an APY figure.

So check which figure your bank is presenting. If the account advertises a 5.12% APY, entering 5.00 reproduces the bank's math, and entering 5.12 would compound it a second time and overstate the ending balance by a small but real margin, about $29 on that $5,000 over 10 years. If instead the bank quotes a nominal rate with monthly compounding, the APY printed beside it already contains the correction; use whichever one you are confident about, never both at once. Wherever the two figures are shown together on a statement, the APY is the one that describes what actually accrues. If the two figures disagree, the APY is the one that describes money actually accruing.

The balance is nominal; your groceries are not

The ending value this calculator produces is in nominal dollars: it says nothing about what those dollars will buy. Take $5,000 at 5% for 10 years, which reaches about $8,144. If prices had risen 2.5% each year over the same decade, $8,144 then is worth about 8,144 divided by 1.025 to the 10th, roughly $6,374 in today's purchasing power. The gap between $8,144 and $6,374 is real money, and no field on the calculator captures it.

The 2.5% figure is illustrative; actual inflation varies year to year and no one issues a correct ten-year forecast in advance. But the adjustment direction is not an assumption, it is arithmetic, and it is the honest denominator for any goal expressed in today's costs, such as a down payment number you currently see. Run the calculator once for the nominal value, then divide the result by (1 plus the inflation rate you choose) to the power of years. If the real value is lower than your goal, the response belongs in the rate or contribution, not in hoping inflation behaves. Same division, different goal, and the conclusion usually points at the contribution rather than the rate.

The model assumes the balance sits still and the rate does too

The compounding formula on this page works on a single starting amount that receives no additions and no withdrawals, at one unchanging rate, for the whole term. A real account drifts from that picture in common ways: a promotional 5% for the first 12 months that reverts to a standard rate, monthly deposits of savings you shovel in, or a withdrawal that resets part of the curve.

Each of those needs a different move rather than a bigger assumption. For a rate that changes, run one calculation to the changeover month at the intro rate, then use that ending value as the starting principal of a second run at the ongoing rate for the remaining months; the sum of the two is close to the true path. For monthly additions, this page will understate the outcome, because added money earns from the day it lands; the recurring-contributions calculator is the right tool there. For withdrawals, the practical approximation is to subtract the withdrawn amount and reduce the years accordingly. None of these workarounds are perfect, but each is closer than entering the intro rate and letting it run for 10 years.

Tax on the interest is not in the ending value

In a taxable account, bank interest is generally taxable in the year it is received, which means the compounding shown here overstates what stays yours. On the $5,000 at 5% for 10 years, the total interest realized is about $3,144, and it accrues year by year, with each year's figure reported on a 1099-INT. The calculator's final line is before any of that.

The cleanest way to price it is an after-tax rate. If your marginal rate is an illustrative 25%, the interest compounding for you is effectively 5% times 0.75, or 3.75%, and entering that figure produces a more usable ending value. The difference is not trivial: 3.75% versus 5% over 10 years on the same $5,000 is roughly $720 of ending balance. Tax-advantaged accounts flip this arrangement, which is why the same rate can be a different real return depending on where the money sits. Two practical habits: keep each year's 1099-INT so the cumulative interest is reconcilable when the account is eventually closed, and enter the after-tax rate when the account is taxable. The same interest is a different return depending on which type of account it compounds in, and the calculator cannot tell them apart.