Investment Calculator: Contributions, Withdrawals & Inflation

Compound growth

Future value = starting amount × (1 + return)^years

Your returns earn returns of their own. $10,000 growing 7% a year becomes $19.7K in 10 years. Monthly contributions are added each month and compound the same way.

Small amounts add up

$500 a month for 30 years is $180K put in. At the stock market's historical average of 10.0%, it grows to about $1M. Raising the amount 3% a year, roughly in line with pay raises, makes it about $1.4M.

Averages vs. real life

Markets don't rise smoothly. The same $500 a month in the S&P 500 for 30 years ended between $773.1K (starting 1952) and $3.2M (starting 1970) across history. The calculator's reality-check section shows this range for your plan.

Inflation and today's dollars

Prices rise over time, so a future balance buys less than the same amount today. The “today's dollars” figure divides out inflation, at 3.0% a year by default (the long-run average).

The rule of 72

Divide 72 by your yearly return to estimate how long money takes to double. At 10.0%, about 7 years; at 4%, about 18 years.

What it leaves out

Fund fees, taxes and withdrawals aren't included. Retirement accounts like a 401(k) or IRA can delay or avoid taxes on growth. See your take-home pay after 401(k) contributions in the paycheck calculator.

What rate of return should I use?

It depends on what you invest in. From 1928 to 2025, U.S. stocks averaged 10.0% a year, bonds 4.5% and Treasury bills 3.4%. Many people plan with a lower number, like 6–7% for stocks, to be cautious.

How much will $500 a month be worth in 30 years?

About $1M at 10.0% a year, from $180K put in. In real history it ranged from $773.1K to $3.2M, with a typical result of $1.2M.

Is the stock market's average return guaranteed?

No. Stocks can fall sharply for years. In every historical 30-year periods, $500 a month in stocks still ended above the money put in, but the past doesn't guarantee the future.

Is a 10% return realistic?

As a very long-run average for U.S. stocks, it has been: 10.0% a year from 1928 to 2025, before fees, taxes and inflation. After inflation it was closer to 6.8%. Individual decades have been much better or much worse, which is why the reality-check section shows the range.

Is this adjusted for inflation?

Both are shown. The main number is in future dollars; “in today's dollars” removes inflation (change the rate under more options). The reality check uses the inflation that actually happened in each period.

Are taxes and fees included?

No. Subtract your fund's expense ratio from the return to include fees (for example 7% − 0.5% = 6.5%). Taxes depend on the account: 401(k)s and IRAs defer or avoid tax on growth, while taxable accounts owe tax on dividends and gains.

How long will my money last if I withdraw every month?

Turn on more options and enter a monthly withdrawal and the year it starts. The calculator stops contributions then and tells you if the money runs out, and the reality check shows how often that happened in real history.

How much should I increase my contributions each year?

Many people raise them with their pay, often 2–3% a year, or put part of every raise toward investing. The “raise contributions” option shows the effect.

What does compounding monthly mean here?

Returns are applied every month at a rate that adds up to the yearly return you chose, and each monthly deposit starts growing right away (or at the month's end if you change that option).