Investment Calculator
Free investment calculator. Project how a lump sum plus monthly contributions grow over time, with CAGR and inflation-adjusted values. No signup.
What is an investment calculator?
An investment calculator projects how a starting balance plus regular contributions grow over time with compound returns. It shows the future value, how much of it is your own money, how much is growth, and the true annualized return (CAGR).
How this calculator works
- Enter a starting balance, a monthly contribution, the number of years, and an expected annual return.
- It compounds monthly — the way most brokerage and retirement accounts accrue.
- Future value is split into contributions and investment growth so you can see the compounding effect plainly.
- An inflation input converts the result into today’s purchasing power.
How to use the result
- Focus on the inflation-adjusted number — it’s the real spending power you’ll have, not the nominal total.
- Compare the growth against contributions. If growth is a small slice, your time horizon or contribution is doing the heavy lifting — compound returns need years.
- Use the CAGR to compare this projection honestly with alternatives like paying down debt at a known rate.
- Re-run whenever your income changes and increase the contribution — early dollars compound the longest.
How does compound interest grow investments?
Each year you earn returns on both your contributions and the returns from previous years. At 7% annualized, money roughly doubles every 10 years by the rule of 72. That’s why a $10,000 start plus $500 a month can pass $300,000 after 20 years — more than half of it pure growth.
Common mistakes
- Entering nominal returns without inflation. 7% nominal is roughly 4.5% in real terms at 2.5% inflation — the real number is what you can spend.
- Ignoring fees and taxes. Subtract expense ratios and expected tax from your return assumption.
- Assuming steady returns. Real markets swing; the projection is a long-run average, not a path.
The same compounding engine drives retirement planning — the retirement calculator adds the age timeline and monthly-income estimate. If you’re torn between investing and paying off a loan, compare the loan’s rate to your expected return with the simple loan calculator.