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Investment Calculator

Estimate how a lump sum and regular monthly investing could grow, with a year-by-year table.

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This is an estimate, not financial advice. It assumes a steady return with monthly compounding and contributions at the end of each month. Real returns go up and down, you can lose money, and tax, fees and inflation are not included.

Quick Answer

An investment grows from its starting amount and regular additions. If you start with $10,000 and add $500 a month at a 7% yearly return, compounded monthly, you could have about $300,851 after 20 years. Of that, $130,000 is money you put in.

Last updated: 2 November 2026 ·How we calculate this: monthly compound growth formula

Table of Contents

How This Investment Calculator Works

This calculator estimates how money grows when returns are added and then earn returns themselves. It is built for regular investing, so you can see the effect of monthly contributions over time.

Quick explanation: balance = growth on your starting amount + growth on your monthly contributions.

  • Return: a steady yearly rate. Real returns change each year.
  • Contributions: added at the end of each month.
  • Table: shows your balance after each year.

How to Use the Investment Calculator

  1. Enter the amount you have to invest today, or 0 if you are starting from nothing.
  2. Enter how much you plan to add each month.
  3. Enter a yearly return you think is realistic. Try a low, middle and high rate.
  4. Enter how many years you plan to invest, then press Calculate.
  5. Read the year-by-year table to see how much comes from your money and how much from growth.

Core Formulas

  • Monthly rate: r = yearly return ÷ 12
  • Future value: FV = P × (1 + r) ^ n + M × ((1 + r) ^ n − 1) ÷ r
  • With a 0% return: FV = P + M × n

P is the starting amount, M is the monthly contribution, and n is the number of months.

Worked Example

You invest $300 a month for 10 years at a 5% yearly return, with no starting amount.

  • Number of months = 120
  • Total put in = $36,000
  • Estimated balance = $46,584.68

Real-Life Examples

  • Starting early: $300 a month at 7% for 40 years (age 25 to 65) could grow to about $787,444. Starting at 35 and investing for 30 years gives about $365,991. The extra $36,000 put in leads to about $421,453 more.
  • Adding a little more: over 25 years at 6%, $500 a month could reach about $346,497. Raising it to $600 a month gives about $415,796.
  • A lump sum on its own: $20,000 left for 15 years at 5%, with nothing added, could grow to about $42,274.
  • Saving for college: $200 a month from birth to age 18 at 6% could reach about $77,471, of which $43,200 is money you put in.

Investing vs Keeping Cash in Savings

  • Return: investments such as stock funds have usually grown faster than savings accounts over long periods, but with no guarantee.
  • Risk: a savings account balance does not fall. An investment can lose value, sometimes for years.
  • Time: money you need within a few years is often safer in savings or a CD. Long-term money has more time to recover from falls.
  • Use both: many people keep an emergency fund in savings and invest money for long-term goals.

Value of $500 a Month Over Time

Estimated balance with no starting amount, compounded monthly, before tax, fees and inflation.

Yearly return10 years20 years30 years
4%$73,625$183,387$347,025
6%$81,940$231,020$502,258
8%$91,473$294,510$745,180
10%$102,422$379,684$1,130,244

What Can Change Your Result

  • Market returns: values can fall as well as rise.
  • Fees: even small yearly fees can reduce growth over time.
  • Taxes: these depend on your account type and location.
  • Inflation: a future balance buys less than the same amount today.

Common Mistakes to Avoid

  • Using one high return. Test several rates, and plan with a cautious one.
  • Ignoring fees. With $500 a month for 30 years, a 7% return gives about $609,985. A 1% yearly fee that cuts it to 6% leaves about $502,258.
  • Forgetting inflation. A future balance buys less than the same amount today.
  • Stopping during market falls. Pausing contributions when prices are low can lower long-term results.
  • Skipping tax-advantaged accounts. Accounts such as a 401(k) or IRA can help your money grow with less tax.

Frequently Asked Questions

Grow your starting amount by the return each period, then add the growth on each contribution. This calculator does both.

At a 7% yearly return for 20 years, with $10,000 to start, it could reach about $300,851. Results change with your return.

Use a rate you consider realistic, and test a few rates. Returns are never guaranteed.

This one focuses on regular monthly investing, with a yearly table of what you put in and what you have.

No. Both will lower your real result.

At a 7% yearly return for 30 years, starting from zero, you would need to invest about $820 a month.

Investing a lump sum early gives it more time in the market. Monthly investing spreads out your buying and can be easier on a budget. Both work with this calculator.

Inflation lowers what your future balance can buy. To see results in today's money, subtract the expected inflation rate from your return.

Use a total return that includes reinvested dividends and interest. This calculator assumes all earnings stay invested and keep growing.

It compounds monthly and adds your contribution at the end of each month. Yearly compounding gives a slightly lower result with the same rate.

References & Sources

SourceUsed ForLink
U.S. SEC, Investor.gov compound interest calculator How compounding grows savings. https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator
Wikipedia, Future value Future value formulas. https://en.wikipedia.org/wiki/Future_value