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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 requiredNo signup, no paywall
$5,000
$0$50k$100k
$500/mo
$0$1,000$2,500$5,000
20 yrs
3y20y40y
7%
3%7%12%
Note on AssumptionsThis is a single assumed annual return with no separate inflation adjustment applied. Historically, broad U.S. stock index funds have averaged roughly 10% annualized nominal return, or roughly 7% once a ~3% long-run inflation rate is backed out. Whether the number you pick represents nominal or inflation-adjusted growth is your assumption to make, not a fact this calculator asserts.
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
2.2× growth multiplier

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, your contributions usually make up most of the balance. As the balance grows, investment returns can eventually contribute more to annual growth than new deposits. When that happens depends on the starting balance, contribution amount, assumed return, and time horizon.

Nominal vs. Inflation-Adjusted Returns

This calculator applies one assumed annual return and does not subtract inflation for you. Over the last century, the S&P 500 has averaged roughly 10% annualized nominal return, while inflation has historically averaged roughly 3% annually. Some people use a lower number, such as 7%, as a rough stand-in for growth in today’s purchasing power — but that 7% is not itself a special or guaranteed “real” return, and future inflation and market returns can differ from historical averages. Pick a number you understand, and be consistent about whether you’re treating it as nominal or inflation-adjusted.

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