Investment growth calculator

Enter a starting amount, a monthly contribution and a return you choose. You get a year-by-year table and chart, and the final figure in future dollars and in today's money after inflation.

Added at the end of each month.
5% is an assumption to get you started, not a forecast and not a promise. Nobody knows future returns. Try a lower figure too, or a negative one such as -3.
Starts at 3.4%, the rise in consumer prices over the 12 months to August 2026. Future inflation will differ. Clear the box to skip it.
Investment growth estimateAssumes 5% a year
Balance after 20 years, in future dollars
$135,008

In today's money that is about $69,175, if prices rise 3.4% a year.

Future dollars$135,008the number on the statement in 20 years
Today's money$69,175what that buys at today's prices
Year 1Year 20
money you paid ingrowth
Starting amount
$5,000
Monthly contributions (240 × $300)
$72,000
Growth
$58,008
Balance in future dollars
$135,008
In today's money (3.4% inflation)
$69,175
If the return were 3% a year
$107,087
If the return were 7% a year
$171,609

This is not a forecast. Returns are not guaranteed, they change from year to year, and investments can lose value. Fees and taxes are not deducted.

The sum uses the same return every year, which no real investment delivers. The lower and higher lines show how far the result moves when the return is 2 points either side of your figure.

CheckMySum. Printed . This is an estimate, not tax, legal or financial advice.

Year-by-year table

These are the numbers behind the chart. They change as you change the inputs above.

Assumes 5% a year and 3.4% inflation. Contributions are added at the end of each month.
End of yearPaid in so farGrowth so farBalanceIn today's money
1$8,600$332$8,932$8,638
2$12,200$860$13,060$12,215
3$15,800$1,595$17,395$15,735
4$19,400$2,546$21,946$19,199
5$23,000$3,726$26,726$22,611
6$26,600$5,144$31,744$25,974
7$30,200$6,813$37,013$29,289
8$33,800$8,745$42,545$32,560
9$37,400$10,954$48,354$35,789
10$41,000$13,453$54,453$38,978
11$44,600$16,258$60,858$42,130
12$48,200$19,383$67,583$45,247
13$51,800$22,843$74,643$48,331
14$55,400$26,657$82,057$51,384
15$59,000$30,842$89,842$54,409
16$62,600$35,416$98,016$57,407
17$66,200$40,398$106,598$60,381
18$69,800$45,810$115,610$63,332
19$73,400$51,672$125,072$66,263
20$77,000$58,008$135,008$69,175

Short answer: $5,000 plus $300 a month, at an assumed return of 5% a year, would reach about $135,008 in 20 years. With 3.4% inflation that buys what $69,175 buys today. Both numbers depend on the return you assume. Returns are not guaranteed, and investments can lose value.

How investment growth is calculated

The calculator applies the return you enter to the balance, adds your contribution, and repeats for every month. It is a projection of one assumption, not a prediction of what a market will do.

  1. Turn the yearly return into a monthly one. A 5% yearly return means the balance is 5% higher after 12 months, so one month is the twelfth root.
    Monthly growth = (1 + yearly return)^(1/12)
  2. Grow the balance and add the contribution. The contribution goes in at the end of the month, so it starts to grow the month after.
    New balance = old balance × monthly growth + monthly contribution
  3. Record each year. The table shows what you have paid in, the growth so far and the balance at the end of every year.
  4. Take out inflation. The balance is divided by (1 + inflation) once for each year that has passed.
    Today's money = future balance ÷ (1 + inflation)^years
  5. Run a lower and a higher case. The same sum is repeated with the return 2 points below and 2 points above your figure.

Worked examples

Every return and inflation rate below is an assumption chosen to show the sums. Real results will be different, and can be lower than the lower case shown.

$5,000 plus $300 a month for 20 years

Assumes 5% a year and 3.4% inflation. These are the calculator's starting numbers.

  • Total paid in$77,000
  • Growth$58,008
  • Balance in future dollars$135,008
  • If the return were 3% a year$107,087
  • If the return were 7% a year$171,609
  • Return after inflation1.55% a year
  • In today's money (3.4% inflation)$69,175

$500 a month for 30 years, starting from nothing

Assumes 6% a year, with inflation at the Federal Reserve's longer-run goal of 2%. Over a long stretch the gap between the lower and higher case becomes very wide.

  • Total paid in$180,000
  • Growth$307,256
  • Balance in future dollars$487,256
  • If the return were 4% a year$342,635
  • If the return were 8% a year$704,275
  • Return after inflation3.92% a year
  • In today's money (2% inflation)$269,000

A falling market: $20,000 plus $200 a month for 3 years

Assumes a loss of 3% a year and 3% inflation. You end with less than you paid in, and that amount also buys less.

  • Total paid in$27,200
  • Loss−$2,057
  • Balance in future dollars$25,143
  • If the return were −5% a year$23,835
  • If the return were −1% a year$26,501
  • Return after inflation−5.83% a year
  • In today's money (3% inflation)$23,009

What a monthly contribution could grow to

This table starts from zero and assumes 5% a year. The last column takes 3.4% inflation out of the 30-year figure.

Assumes a 5% yearly return every year and 3.4% inflation. Both are assumptions for illustration, not forecasts. No fees or taxes.
Monthly contributionAfter 10 yearsAfter 20 yearsAfter 30 years30 years, in today's money
$100$15,436$40,580$81,538$29,905
$200$30,873$81,161$163,075$59,810
$300$46,309$121,741$244,613$89,715
$500$77,182$202,902$407,688$149,524
$750$115,772$304,353$611,532$224,286
$1,000$154,363$405,804$815,376$299,049

At $300 a month, ten more years takes the result from $121,741 to $244,613. The extra contributions are $36,000. The rest of the difference is growth, most of it on money that was already invested. That is why starting early matters in a projection like this.

Choosing a return assumption

The return is the input that moves the result most, and it is the one nobody can know. The calculator starts at 5% so that it shows a result. That figure is not a forecast and is not based on any product.

What the US Securities and Exchange Commission says about risk and return is worth reading before you pick a number:

  • All investments involve some degree of risk.
  • The potential for greater returns comes with greater risk.
  • Large company stocks as a group have lost money on average about one out of every three years.
  • Investors who stayed with stocks over long periods, such as 15 years, have generally been rewarded with strong, positive returns. That describes the past. There is no guarantee it will continue.
  • Securities are not insured against a loss in value. FDIC insurance covers deposits only.

Three habits make the projection more honest:

  • Look at the lower case first. If your plan only works at the higher figure, it depends on luck.
  • Match the return to what you hold. Cash, bonds and stocks have different risks, so one rate does not suit all of them.
  • Remember that real returns are uneven. A steady 5% every year is a smooth line through years that will be better and worse. A bad year close to the date you need the money matters more than a bad year at the start.

Be wary of anyone who promises a high return with little or no risk. The SEC lists that pitch as a common feature of investment fraud.

Future dollars and today's money

A projection 20 or 30 years out produces large numbers, and part of their size is higher prices. In the first example, the balance of $135,008 buys what $69,175 buys now. The difference, $65,833, is inflation and not extra wealth.

You can also think of it as a lower return. A 5% return with 3.4% inflation is a return of about 1.55% a year in buying power.

Return after inflation = (1 + return) ÷ (1 + inflation) − 1

The inflation box starts at 3.4%, the rise in the Consumer Price Index over the 12 months to August 2026. One year's figure is a weak guide to the next 20. The Federal Reserve aims for inflation of 2% a year over the longer run, so that is another figure worth trying.

Fees and time

Fees come out of the return every year, so they compound in the same way growth does. The SEC gives an example of $100,000 growing at 4% a year for 20 years. With a yearly fee of 0.25% the portfolio ends at about $208,000. With a 1% fee it ends at about $179,000.

This calculator has no fee box. Subtract the yearly fee from the return you enter. With no starting amount, $300 a month for 30 years comes to $244,613 at 5%. Enter 4% to allow for a 1% fee and it comes to $205,581.

What the result leaves out

  • Ups and downs. The same return is applied every year. Real investments rise and fall.
  • Fees. None are deducted unless you lower the return yourself.
  • Taxes. Nothing is deducted for tax on dividends, interest or gains, or on withdrawals from a retirement account.
  • Contribution limits. Retirement accounts have yearly limits. This tool does not check them.
  • Changing contributions. The monthly amount stays the same. It does not rise with your pay.

Common mistakes

  • Reading the result as a forecast. It shows what one assumed rate produces. Nothing more.
  • Picking the return that gives the answer you want. Raising the rate does not make the plan safer.
  • Quoting the future-dollar figure on its own. For a goal many years away, the figure in today's money is the one to plan around.
  • Leaving out fees. A 1% yearly fee is a full point off the return, every year.
  • Using money you will need soon. A projection over 20 years says nothing about where the balance will be in year two.

Questions people ask

What return should I assume?

There is no correct figure, because nobody knows future returns. Enter a rate you can defend, run a lower one as well, and treat the gap between the two as part of the answer. The 5% starting value is an assumption, not a forecast.

Are investment returns guaranteed?

No. The US Securities and Exchange Commission says all investments involve some degree of risk, and that you can lose money you invest in stocks. Securities are not insured against a fall in value.

What does "in today's money" mean?

It is the future balance adjusted for inflation, so it shows what that money would buy at today's prices. The future-dollar figure is the number you would see on a statement.

How much will $300 a month be worth in 20 years?

At an assumed 5% a year it comes to about $121,741, of which $72,000 is money paid in. At 3% it would be about $98,056. Neither figure is a prediction.

Does the calculator include fees?

No. To allow for a yearly fee, subtract it from the return you enter. A fund expected to return 5% with a 1% yearly fee can be entered as 4%.

Does it include taxes?

No. Tax depends on the type of account and on your income. Growth in a taxable account, a traditional retirement account and a Roth account is treated differently, so the amount you keep can be lower than the figure shown.

Can I enter a negative return?

Yes. Type a minus sign in front of the number. This shows what happens to your contributions if the investment loses value each year.

Is this the same as a compound interest calculator?

The maths is the same. The difference is what the rate means. Interest on a bank account is set by the bank and paid on insured deposits. An investment return is uncertain and can be negative in any year.

Sources

Figures last checked against these sources on October 10, 2026. This page gives general information and estimates, not tax, legal or financial advice.