Free Investment
Calculator

The calculator above answers one question: if you start with a lump sum and add to it every month, what could it be worth later? It needs four inputs.

1. Starting amount: what you have invested today. Enter 0 if you are starting from nothing.
2. Monthly contribution: what you plan to add each month.
3. Expected annual return: the average yearly growth you want to test.
4. Years to grow: how long the money stays invested.

With the default inputs ($10,000 to start, $500 a month, 8% a year, 20 years) the result is $345,742. Of that, $130,000 is money you put in and $215,742 is growth. The calculator compounds monthly and assumes each contribution is made at the start of the month.

Change one input at a time to see what matters most. Leaving the money for 30 years instead of 20 takes the result to about $859,500. Raising the contribution from $500 to $750 a month takes it to about $494,000. Most of the difference between those two comes from time, because growth is earned on earlier growth: that is compound interest.

The rate of return moves the result more than any other input, and nobody knows it in advance. The S&P 500 has produced an average annual total return of roughly 10% before inflation from 1928 through 2025 (NYU Stern data), which is about 7% after inflation. Single years ranged from large losses to large gains.

Run three cases instead of one. With the default inputs, 6% a year gives about $265,000, 8% gives $345,742 and 10% gives about $456,000. If you want the answer in today's purchasing power, use a rate with inflation already taken out (7% in place of 10%, for example), or convert a future amount with the inflation calculator.

• What does a single deposit grow to, and how much does the compounding frequency matter? Use the compound interest calculator.
• What do monthly contributions add up to, year by year? The dollar cost averaging calculator uses the same method as the one above and adds a chart of invested money against returns over time.
• How much did an investment actually earn, in total and per year? Use the ROI calculator.
• What will a loan cost each month, and in interest over its life? Use the loan payment calculator.
• Are you saving enough to retire, and how much a month would close the gap? Use the retirement calculator.
• What will today's dollars buy later? Use the inflation calculator.
• What did a stock trade make after fees, and where is break-even? Use the stock profit and loss calculator.
• How much do you need to stop working, and how long until you get there? Use the FIRE calculator.

The calculator guide compares all eight side by side.

Every result here is arithmetic on the inputs you choose. Real returns arrive unevenly, and a result does not account for taxes, fees or inflation unless the calculator says it does. Treat a projection as a way to compare choices, such as starting now against starting in five years, not as a forecast.

These tools are a starting point, not a substitute for personalized advice. For a decision involving a large sum, a financial advisor can weigh your taxes, goals and tolerance for risk. The About page explains how the numbers are checked.