Investment Calculator
Model investment growth from a starting amount, regular contributions, compounding frequency and return, with a year-by-year table.
🔒 Runs entirely in your browser — nothing is uploadedThe investment growth formula
An investment grows by compounding: returns are reinvested so they earn further returns. For a one-time lump sum the standard formula is A = P(1 + r/n)nt, where P is the starting amount, r is the annual return as a decimal, n is the number of compounding periods per year and t is the number of years. Regular contributions add a second layer. Each compounding period the existing balance grows, and then a contribution is deposited; over time those deposits compound too, following the future value of a series. This calculator steps through every period and also rolls the results up into the year-by-year table below so you can see the balance climb.
Reading the year-by-year table
The table breaks the projection into annual rows. The invested column is the cumulative money you have put in — your initial amount plus every contribution to that point. The growth column is the cumulative return earned, the difference between your balance and what you contributed. The balance column is the running total at the end of each year. Early on, contributions usually dominate the balance; later, growth takes over as compounding accelerates. That crossover is the visual heart of long-term investing and a strong argument for starting early and staying invested through the full horizon rather than trying to time entries and exits.
Assumptions and risk
This tool assumes a constant return every period, but real markets are volatile: actual results vary year to year and investments can lose value. The figure you enter is nominal — to think in today's purchasing power, subtract your inflation expectation to get a real return. The model excludes taxes, trading fees, fund expense ratios and irregular deposits, all of which affect net outcomes. Because everything runs locally in your browser with no account or live data feed, it is ideal for private "what if" comparisons. Treat the numbers as an educational estimate, not advice, and confirm a full plan with a qualified professional.
How to use
- Enter the starting amountType your initial investment, the annual return and the number of years.
- Add contributionsOptionally add a regular contribution and choose how often interest compounds.
- Read the growth tableReview the final balance and a year-by-year breakdown of contributions, growth and balance.