Monthly Contribution Calculator

FV = starting balance × (1 + i)ⁿ + contributions × [((1 + i)ⁿ − 1) ÷ i]; i = monthly rate, n = months

How regular saving adds up

Putting a fixed amount aside every month is the most reliable way most people build savings — for a house deposit, a child’s education, or retirement. This calculator projects that habit forward: it grows any starting balance and every monthly contribution at the rate you set, and splits the result into what you put in versus the interest it earned.

The maths is an annuity sitting on top of a lumpsum: your starting balance compounds for the full term, while each monthly contribution compounds from the month you pay it in. Because the earliest money has the longest to grow, the interest band on the chart starts small and then climbs steeply — the late-year growth is doing far more than your monthly deposit. The expected rate is your assumption; real returns vary, so treat the figure as a central estimate.

Worked example — $500 a month at 7% for 30 years, nothing to start: You contribute 360 × $500 = $180,000. It grows to roughly $610,000 — so about $430,000 of the final balance is interest, more than twice what you paid in.

Starting balance, step-up and timing

A starting balance is anything you have already saved; it sits at the base of the contributions band and compounds for the whole period, so even a modest head start makes a visible difference by the end. When you enter one, the calculator also shows a growth split — how much of the final balance came from that initial amount versus from your monthly contributions.

An annual increase steps your contribution up each year to track a rising income, which lifts the final balance more than the small yearly bumps suggest. Contribution timing controls whether each month’s money goes in at the start or the end of the month; start-of-month gives every contribution one extra month of growth, so it ends a little higher.

Inflation and tax

A large future balance is not the same as large spending power. Inflation erodes what each unit of currency buys, so the calculator can discount the final balance back to today’s money — the “real balance”. Over a 30-year horizon that adjustment is substantial, and it is the figure worth planning around.

Tax can take a second bite, depending on the account: interest or gains in a taxable account are reduced by your rate, while a tax-sheltered retirement or ISA-style account may owe nothing. Enter a rate to see the after-tax balance; leave it at zero for sheltered savings.

How this differs from the SIP and compound interest tools

The underlying maths — the future value of regular contributions — is the same one the SIP calculator uses; this version simply frames it as general saving rather than mutual-fund investing, and leads with the starting-balance and growth-split view. If you want deposits and withdrawals, or a deposit-first layout, the Compound Interest calculator is more general; for drawing an income from the pot later, see the 4% Rule calculator.