Use this free compound interest and growth calculator to see how a starting amount plus regular contributions can grow over time — and how much of the result is growth versus what you put in.
How the compound growth calculator works
Enter a starting amount, a regular contribution, an expected annual return, and a time horizon. The tool compounds your balance each period and adds your contributions to project a future value.
The compound growth formula
Future value = P × (1 + i)ⁿ + C × [((1 + i)ⁿ − 1) ÷ i], where P is your starting amount, C is your contribution per period, i is the annual return divided by periods per year, and n is the number of periods. Results are nominal and before inflation, fees, and taxes.
Frequently asked questions
Is the return guaranteed?
No. A constant annual return is modeled; real returns vary and can be negative.
Does it account for inflation or fees?
No — the figure is nominal and before fees and taxes, which reduce real growth.
How often does it compound?
Monthly or annually, matching the contribution frequency you choose.
Educational tool, not financial advice. Projections are illustrative and not a forecast.
Where to invest: brokers with fractional shares
To act on what this tool shows you, you’ll need a brokerage account. These are established brokers we use that support fractional shares — buying a slice of a share by dollar amount, which makes dollar-cost averaging and diversifying with small amounts easy:
- Charles Schwab — full-service broker whose “Stock Slices” let you buy fractional shares of S&P 500 companies from $5.
- Fidelity — “Stocks by the Slice” fractional investing from $1, with strong research and low-cost index funds.
Referral disclosure: the broker links above are referral links. If you open and fund an account through them we may receive a referral reward at no cost to you; it never affects our tools or conclusions. This is educational information, not investment advice — choose the broker that best fits your needs.