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Jon Curry

The Next Dollar · Calculator

Investment Growth Calculator

Understand the math of consistent compound growth without hype. Adjust your timeline, starting amount, and monthly additions to see how principal separates from compound interest.

Start Here · Core Tool

Investment Growth Calculator

Zero login requiredConservative real returns
$5,000
$0$50k$100k
$500/mo
$0$1,000$2,500$5,000
20 yrs
3y20y40y
7%
3% (bonds)7% (real)10% (nominal)
Note on AssumptionsHistorically, broad index funds (e.g. S&P 500 or Total US Stock Market) have averaged ~10% nominal annual return, or ~7% after inflation. Using 7% yields numbers in today’s purchasing power.
Projected Outcome (20 Years)
$280,657
Total You Put In
$125,000
45% of total
Compound Growth
+$155,657
55% from compounding
Growth Trajectory (0 to 20y)2.2× multiplier
$281kYr 0Yr 10Yr 20
Total balance (with growth)Your direct contributions

Methodology & Math

How Compounding Works Over Decades

This calculator uses monthly compound interest calculated as:

A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)]

In the early years (0–7 years), your contributions represent the vast majority of your portfolio. Around year 10 to 15, the rate of compounding begins to outpace your annual deposits, causing the curve to bend dramatically upward.

Why Real Returns Matter (7% vs 10%)

Over the last 100 years, the S&P 500 has yielded approximately 10% annualized nominal return. However, inflation historically averages ~3% annually. Setting the return slider to 7% provides an estimate in today’s dollars, giving you an honest representation of your future purchasing power.

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