Investment Calculator
Project how a lump sum plus regular contributions could grow over time.
Your Details
Contributions vs. Growth
What makes up your final balance
- Contributed$50.0K
- Growth$53.0K
Final Balance by Rate of Return
Sensitivity to your assumed return
Balance Growth Over Time
Total balance year by year
Contributed vs. Growth by Year
How growth accelerates over time
How It Works
- Enter your starting balance and regular contribution.
- Enter your expected annual rate of return.
- Set your time horizon in years.
- Press Calculate to update your results and charts.
Formula Used
P = initial investment, r = periodic rate, t = number of periods, PMT = contribution per period.
Good to Know
- • Starting earlier matters more than contributing more later.
- • Small rate differences compound into large gaps over decades.
- • Consistent contributions smooth out market swings.
Important Notes
- • Returns are assumed, not guaranteed.
- • Figures don't account for taxes or fees unless noted.
- • Past performance doesn't predict future results.
Lump Sum vs. Dollar-Cost Averaging
Investing a lump sum immediately tends to outperform spreading it out over time, on average, simply because more money is exposed to growth for longer. Regular contributions (dollar-cost averaging) trade some of that expected return for smoother, less stressful investing — you're buying at a mix of prices rather than betting on a single entry point. This calculator models both together: an initial amount plus ongoing monthly contributions.
Setting a Realistic Rate of Return
The rate you assume matters more than almost any other input here. A diversified stock portfolio has historically returned high single digits annually over long periods, before inflation, though any given decade can look very different. It's worth testing a conservative and an optimistic rate side by side using the sensitivity chart above, rather than anchoring on one number.
Clarifying the Terms
- Lump sum — a one-time initial investment, as opposed to spreading contributions over time.
- Dollar-cost averaging — investing a fixed amount on a regular schedule regardless of price.
Testing It With an Example: Lump Sum Plus Contributions
$5,000 initial investment, $250/month, 8% assumed return, over 15 years:
Growth of $250/month contributions ≈ $85,540
Total future value ≈ $102,070
Total contributed: $5,000 + ($250 × 180) = $50,000. Growth accounts for over half the final balance — a reminder that consistent contributions, not just a strong starting amount, drive much of the long-term outcome.
Return Rate Comparison Table
$5,000 + $250/mo over 15 years, at different return assumptions:
| Return | Future Value |
|---|---|
| 5% | $80,900 |
| 8% | $102,070 |
| 10% | $119,300 |
Things Often Overlooked When Projecting Investments
- Assuming a smooth, constant return — real markets are volatile year to year.
- Ignoring fees and taxes — both reduce the effective return below the assumed rate.