Growth inputs
Adjust each input to see how compounding magnifies long-term differences.
Essential Calculator
Compound Interest Calculator
Project long-term investment growth with recurring contributions and see how compounding changes the curve over time.
How to use this page
- Enter your starting balance, expected return, monthly contribution, and time horizon.
- The chart tracks ending balance each year so growth acceleration is easy to spot.
- Use this to compare delayed investing versus starting now with smaller amounts.
Results
Ending balance$309,510
Total contributions$111,000
Investment growth$198,510
Y20$309,510
What this calculator helps you see
This page is built to make compounding feel tangible. The chart highlights how steady contributions and time often matter more than chasing small changes in return assumptions.
When to use this calculator
Show the value of starting early
Run the same monthly contribution with different start dates to make the cost of waiting visible in actual dollar terms.
Compare contribution strategies
This is useful for testing whether increasing monthly deposits or extending the timeline has a bigger impact on the final outcome.
Formula
FV = P(1 + r/m)^(mt) + PMT × [((1 + r/m)^(mt) - 1) ÷ (r/m)]
P is the starting balance, r is annual return, m is compounding periods per year, t is years, and PMT is the recurring contribution.
Worked example
Starting with $15,000, contributing $400 per month, and earning 8% annually for 20 years creates a much larger ending balance than most people expect when they focus only on contributions.
| Item | Value |
|---|---|
| Starting balance | $15,000 |
| Monthly contribution | $400 |
| Return assumption | 8% |
| Time horizon | 20 years |
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Before you decide
- Outputs are estimates and should be reviewed against lender or plan-specific terms.
- Inputs are intentionally transparent so assumptions are easy to audit.
- Rates, fees, taxes, and account terms can change the final result.
Page details
- Updated April 15, 2026
- For assumptions and general guidance, see Methodology.
- For how explanatory content is written, see Editorial Policy.
Scenario comparison
| Scenario | Contribution | Likely effect |
|---|---|---|
| Start now | $400/month | More years for compound growth |
| Wait 5 years | $400/month | Much lower final balance |
| Increase savings | $550/month | Higher ending balance without changing timeline |
Common questions
Why does the chart curve upward later in the timeline?
As the account balance grows, the same percentage return applies to a larger base, so the annual dollar gain accelerates.
Is a fixed annual return realistic?
No portfolio earns a smooth fixed return in practice, but a steady estimate is useful for understanding long-run sensitivity and savings discipline.