Savings Goal Calculator
Work out how much to put away each month to hit a savings target — or what a regular monthly amount will have grown to — with interest compounded monthly.
| Starting balance | — |
| Monthly saving | — |
| Total paid in | — |
| Interest earned | — |
| Final balance | — |
Estimate only. Assumes one fixed rate for the whole period, interest added and compounded monthly, and each monthly amount paid in at the end of the month. It ignores tax on interest, inflation, fees, missed months and rate changes, and it is a generic calculator — not financial advice or a recommendation of any account or provider.
How the calculation works
Both modes use the same equation. With i = annual rate ÷ 12 (the monthly rate), n = years × 12 (the number of months), P = starting balance and M = monthly saving, the balance at the end is:
Final balance = P × (1 + i)n + M × [((1 + i)n − 1) ÷ i]
The first term is the starting balance growing with compound interest; the second is the future value of an ordinary annuity — a level payment made at the end of every month, each one earning interest for the months that remain. "Monthly amount needed" simply rearranges this for M: subtract what the starting balance grows to on its own, then divide by the annuity factor. If the rate is 0%, the annuity factor is just n, so the goal is split evenly across the months.
- Are payments assumed at the start or the end of each month?
- At the end (an "ordinary annuity"). If you actually pay in at the start of each month, every payment earns one extra month of interest, so the true final balance is slightly higher — by a factor of (1 + i) — and the monthly amount you need is slightly lower. Over a few years at typical savings rates the difference is small.
- What interest rate should I enter?
- The annual rate before tax. Savings rates change over time, so treat the output as a scenario rather than a promise — running it again with a lower rate gives you a cautious figure. Whether interest is taxed depends on where you live and the type of account, so check the rules that apply to you.
- Why doesn't the monthly figure multiply out exactly to the goal?
- The result is rounded to the penny for display, but the table uses the unrounded value. Paying the rounded amount will land you within a few pence of the target. The goal is also reached only if the rate stays fixed and no month is missed.
FAQ
Sources
Method: future value of an ordinary annuity (level end-of-month payments) plus compound growth of the starting balance, both at the monthly rate i = annual rate ÷ 12 over n = years × 12 months; the goal mode is the same equation solved for the monthly payment. This is pure arithmetic — no interest rates, tax figures or thresholds are built into the page.
- U.S. SEC Investor.gov — Compound Interest Calculator — methodology reference for the "what my savings grow to" mode: it takes the same inputs (initial investment, monthly contribution, length of time in years, estimated annual interest rate and a compound frequency of annually, semiannually, quarterly, monthly or daily). This page fixes compounding at monthly.
- U.S. SEC Investor.gov — Savings Goal Calculator — methodology reference for the "monthly amount needed" mode: it takes a savings goal, initial investment, years to grow, estimated interest rate and compound frequency, and returns how much to contribute each month to reach that goal.