- Compound growth means your returns earn returns — the longer money is invested, the larger the share of the final balance that comes from growth rather than contributions.
- A 1–2 percentage point difference in assumed return compounds into a large gap over 20–30 years.
- This is a nominal (pre-tax, pre-inflation) projection — use it as a starting point, not a guarantee.
- It's the same projection engine used in Hunch's in-app planning tools.
How the compound growth calculator works
Enter a starting balance, a monthly contribution, an expected annual return, and a number of years. The calculator compounds the balance forward month by month, adding both growth and your contribution at each step, and shows how much of the final total came from contributions versus growth.
The math: compound interest with regular contributions
The calculator applies your annual return rate as a monthly rate (annual rate ÷ 12), then each month adds that month's growth plus your contribution to the running balance — so contributions made early get more months to compound than contributions made later. This is the standard future-value-of-an-annuity calculation used by most retirement and savings calculators.
Worked example
Start with $10,000, contribute $500/month, and assume a 7% annual return over 25 years. The balance grows to roughly $441,000 — of which about $160,000 is your own contributions and the remaining $281,000 is growth. Drop the assumed return to 5%, and the same contributions only reach about $314,000 — a reminder of how sensitive long projections are to the return assumption.
Key terms
- Compounding
- Earning returns on both your original investment and on the returns it has already generated.
- Nominal return
- A return figure before adjusting for inflation — the number this calculator uses.
- Contribution
- Money you add to the balance on a regular schedule, separate from any investment growth.
- Future value
- The projected total balance at the end of the time period, combining contributions and growth.