Project investment value from lump sum plus monthly contributions

The Power of Consistent Contributions

Time and regularity matter more than the initial lump sum for long-horizon investing. A 1,000 lump sum plus 200 monthly over 30 years at 7 percent compounds to roughly 250,000 — only 73,000 of which is contributions. The remaining 177,000 is compound growth.

Realistic Return Assumptions

Long-run historical equity returns average roughly 7 percent after inflation. Bond portfolios return 2-4 percent after inflation. A 60/40 stock-bond portfolio typically projects at 5-6 percent real return. Using higher assumptions produces rosier numbers but misleads when compared to history.

Quick example

With initial investment of 1,000 and monthly contribution of 200 (plus annual return of 7 and years of 30), the result is 252,106.13. 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 Initial Investment, Monthly Contribution, Annual Return, and Years. 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

Standard future value formula for a lump sum plus annuity. Monthly rate is annual rate divided by 12; number of periods is years times 12. Results are estimates for illustration purposes only. 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.

Using this well

Treat the output as one point on a wider map. Run it three times — a pessimistic case, a central case, and a stretch case — and plan against the pessimistic one. That habit alone separates people who stick with an investment plan from those who bail at the first wobble.

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. Treat the number as one scenario, not a forecast.