How this works
The calculator solves the future-value equation backwards. Your starting balance grows on its own, so it covers part of the goal; the monthly contribution has to cover whatever's left, and each deposit earns interest for however many months remain. That's why the required monthly amount is always less than simply dividing the shortfall by the number of months — the earlier deposits do extra work.
Where the interest comes from
Enter the rate your account actually pays. Banks quote savings accounts and CDs as APY (Annual Percentage Yield), which already accounts for compounding within the year — that's the number to use here. For short goals under a couple of years, interest barely moves the needle and the monthly amount is what matters. For goals five years and out, interest starts carrying a visible share of the load, shown above.
Match the account to the deadline
Money you need within a year or two belongs somewhere it can't lose value — a high-yield savings account or a CD timed to your deadline. Money for a goal a decade away can tolerate more variation, but this calculator assumes a steady rate, so it models guaranteed-rate products more faithfully than investments whose returns swing. If you're modelling long-term investment growth instead, our compound interest calculator shows the full year-by-year path.
The number that actually decides it
Try changing the rate from 4% to 5% and watch the required monthly contribution barely move. Then shorten the deadline by a year and watch it jump. For most savings goals, your timeline and your contribution do nearly all the work, and chasing a slightly better rate is the smallest lever of the three. Set the monthly transfer to run automatically the day after payday and the goal mostly takes care of itself.