Monthly Investment Goal Calculator

Reaching 100,000 over 10 years at a 7% annual return takes monthly contributions of roughly 578: about 69,000 paid in, plus 31,000 of compound growth. Stretch the horizon to 15 years and the monthly figure drops to about 315.

How to use it

Enter the amount to reach, the number of years available, and an expected annual return. The tool assumes contributions at the end of each month and monthly compounding, the standard approximation for a regular investment plan. It also assumes the starting balance is zero, so the whole target is built from the contributions themselves.

What the result means

The primary figure is the monthly contribution. Total contributions and compound growth are shown separately, and at the defaults the split is about 69,000 contributed against 31,000 of growth. Growth is the smaller share for a long time: on a fixed monthly amount at 7%, cumulative growth does not overtake cumulative contributions until around year 19. Shortening the horizon pushes the contribution up sharply, because there are fewer months and less time for the balance to compound.

What the rate assumption means

Long-run averages for broad equity indices are often quoted around 7% before inflation and lower once inflation is taken out, with cash and bonds sitting below that. The figure is an assumption rather than a projection, and its effect is not symmetric: at a high assumed rate the required contribution looks small, and a shortfall against that rate leaves a larger gap to close than the same shortfall at a lower one.

Quick example

With target amount of 100,000 and years of 10 years (plus annual return of 7%), the result is 577.75.

Which inputs matter most

Two of the three inputs move the answer most. Target Amount scales the contribution proportionally, so doubling it doubles the monthly figure. Years and Annual Return both act through compounding, which makes them non-linear: at the defaults, stretching 10 years to 15 cuts the monthly from 578 to 315, a 45% reduction for a 50% longer horizon. Contribution size is the output here rather than an input.

What's happening under the hood

The tool solves the ordinary annuity formula for the payment: the target divided by the future value annuity factor at the monthly rate, where the monthly rate is the annual rate divided by 12. It assumes contributions at the end of each month and monthly compounding, the standard simplification for a regular plan, and a starting balance of zero. Figures are before tax, and tax treatment varies by the type of account and the country it is held in.