APY Calculator With Monthly Deposits \

The Math Behind Deposits Plus Compounding

The future value of a lump sum follows FV = P(1 + r/n)^nt. When you add monthly deposits, the formula extends to include a future-value-of-annuity component: FV_deposits = D × [((1 + r/n)^nt − 1) / (r/n)], where D is the periodic deposit. The calculator sums both components for your total projected balance.

In practice, a $200 monthly deposit into an account offering an illustrative 4.50% APY grows to approximately $2,454 after one year — about $54 more than the $2,400 you deposited, purely from interest. Over five years the interest component becomes much larger because prior interest is also compounding. At the ten-year mark, interest earned can represent a significant share of the total balance.

Enter your own deposit amount and rate in the calculator to see exactly when earned interest begins outpacing your contributions.

Choosing a Deposit Amount That Fits Your Budget

Savers on personal-finance forums frequently ask whether it is better to start small and increase deposits later or to commit to a fixed monthly amount from day one. The calculator lets you test both approaches. Run it once with your current comfortable contribution, then again with an aspirational figure — the comparison often reveals that even a modest increase of an extra $50 per month compounds into a meaningful difference over three to five years, thanks to the additional interest each extra dollar generates from the moment it is deposited.

Aligning your deposit to your pay cycle also helps consistency. If you are paid biweekly, the weekly deposits calculator may be a better fit because it puts money to work sooner. For a broader view of how APY converts from a nominal rate, the APY vs APR calculator handles the conversion in either direction.

The APY you enter is held constant for the full projection. Your actual rate may change over time, so revisit the calculator when your bank adjusts its rate.