Monthly Investment Goal Calculator

To build 100,000 over 10 years at a 7% annual return, monthly contributions of roughly 578 get you there — about 69,000 total invested plus 31,000 of compound growth. Stretch the horizon to 15 years and the monthly drops to about 310.

How to use it

Enter your target, the number of years you typically need to reach it, and an expected annual return rate. The tool assumes end-of-month contributions and monthly compounding of the return, which is the standard approximation for regular investment plans.

What the result means

The primary figure is the monthly contribution. Total contributions and compound growth are shown separately — early in the period almost all of the growing balance is your own money, but by year 10+ the compound growth typically overtakes contributions. That's the standard 'snowball' pattern.

What the rate assumption means

7% is roughly the long-term average for global equities before inflation; 4-5% is typical after inflation. Cash and bonds sit lower. The higher the rate, the more sensitive the result is to the assumption — so be realistic.

Quick example

With target amount of 100,000 and years of 10 years (plus annual return of 7%), the result is 577.75. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.

Which inputs matter most

You enter Target Amount, Years, and Annual Return. The rate and the time horizon usually dominate — compounding means a small change in either reshapes the final figure more than a similar shift in contribution size. Test this by doubling one input at a time.

What's happening under the hood

Uses the ordinary annuity formula solved for the payment: target divided by the future value annuity factor at the monthly rate. Monthly rate equals annual rate divided by 12. Assumes end-of-month contributions and monthly compounding — the standard simplification for regular investment plans. Pre-tax; add expected tax treatment separately if comparing wrapped vs unwrapped accounts. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.

Why investors run this

Most people's intuition for compounding is wrong — not because the math is hard, but because linear thinking doesn't account for curves. Running numbers through a calculator like this one is the cheapest way to recalibrate that intuition before making an irreversible decision about contribution rate, asset mix, or retirement age.

What this doesn't capture

Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour changes in drawdowns can reduce outcomes below the projection. The number represents one scenario rather than a forecast.