Free and instant — plug in your own numbers.
If you invest $500 a month and earn a steady 6% a year, you would have about $81,940 after 10 years, $231,020 after 20 years and $502,258 after 30 years. You would have put in $180,000 of your own money over those 30 years; the other $322,258 is growth.
The rate makes a big difference. At 4% the 30-year figure is $347,025, and at 8% it is $745,180. None of these returns is guaranteed. Investments that can earn 6% to 8% over long periods can also lose money in any single year, and savings account rates change. Treat the numbers below as a range of outcomes, not a promise.
The full table
These figures assume $500 is added at the end of every month, growth compounds monthly, and the return stays the same every year. Fees and taxes are left out.
| Years | You put in | At 4% | At 6% | At 8% |
|---|---|---|---|---|
| 10 | $60,000 | $73,625 | $81,940 | $91,473 |
| 20 | $120,000 | $183,387 | $231,020 | $294,510 |
| 30 | $180,000 | $347,025 | $502,258 | $745,180 |
Over 10 years the rate barely seems to matter: the gap between 4% and 8% is under $18,000. Over 30 years it is almost $400,000. Time turns small differences in return into large differences in wealth.
You can rerun any row with your own amount and rate in the compound interest calculator.
How much of it is your money?
Early on, almost all of your balance is money you deposited. Later, growth takes over.
| Years | At 4% | At 6% | At 8% |
|---|---|---|---|
| 10 | 19% growth | 27% growth | 34% growth |
| 20 | 35% growth | 48% growth | 59% growth |
| 30 | 48% growth | 64% growth | 76% growth |
There is a useful milestone hidden in these numbers: the point where total growth overtakes total deposits. At 8%, that happens after about 16 years. At 6%, it takes about 21 years. At 4%, it doesn't happen until about 32 years, just past the end of the table.
Key idea Each decade adds the same $60,000 of deposits, but at 6% the first decade grows your balance by $81,940, the second by $149,080 and the third by $271,238. The final years do the heaviest lifting, so the years you stay invested matter as much as the amount.
That pattern is the same one behind the Rule of 72: at 6%, money doubles roughly every 12 years, and every doubling is bigger than the one before.
The cost of waiting five years
Suppose you plan to start "once things settle down" and end up investing for 25 years instead of 30. You save $30,000 less in deposits, but you lose far more than that.
| Rate | 25 years | 30 years | Cost of the 5-year delay |
|---|---|---|---|
| 4% | $257,065 | $347,025 | $89,960 |
| 6% | $346,497 | $502,258 | $155,761 |
| 8% | $475,513 | $745,180 | $269,667 |
At 6%, the five missing years cost $155,761, more than five times the $30,000 you didn't deposit. The lost years come off the end of the timeline, where growth is largest.
What if you raise the $500 each year?
Few people save exactly the same amount for 30 years. If your income rises, you might increase your monthly deposit by 3% each year: $500 a month in year one, $515 in year two, and so on, reaching $1,178.28 a month in year 30.
| Rate | Flat $500 a month | $500 rising 3% a year |
|---|---|---|
| 4% | $347,025 | $504,210 |
| 6% | $502,258 | $700,020 |
| 8% | $745,180 | $999,347 |
With the annual increase you deposit $285,452 in total instead of $180,000. At 6%, that extra $105,452 adds $197,762 to the final balance. Linking increases to pay rises is one of the least painful ways to save more, because you never see the money in your spending budget.
Starting with a lump sum
If you already have $5,000 to invest on day one, it grows alongside your monthly deposits. At 6% over 30 years, that $5,000 alone grows to about six times its size, lifting your total from $502,258 to $532,370. At 4% the total becomes $363,592, and at 8% it becomes $799,858. A starting balance helps, but the monthly habit does most of the work.
What the money will be worth in today's dollars
A dollar in 30 years will buy less than a dollar today. If prices rise at an illustrative 2.5% a year, here is what each balance would be worth in today's money:
| Years | At 4% | At 6% | At 8% |
|---|---|---|---|
| 10 | $57,516 | $64,011 | $71,459 |
| 20 | $111,916 | $140,985 | $179,731 |
| 30 | $165,441 | $239,448 | $355,259 |
The 6% balance of $502,258 after 30 years would buy roughly what $239,448 buys now. That is still well above the $180,000 you put in, but it is a more honest number to plan around. Try other inflation rates in the inflation calculator, and see what inflation really does to your savings for the full picture.
Which return should you plan with?
The right rate depends on where the money sits.
- Savings accounts and CDs: low risk, and your deposits are protected up to insured limits, but rates are variable or fixed only for short terms. They rise and fall with the wider interest-rate environment, can sit well below 4% for years at a time, and can trail inflation.
- A mix of stocks and bonds: higher expected long-run returns, with real swings along the way. A balanced portfolio might reasonably be modeled somewhere between 4% and 6%.
- Mostly stocks: the highest expected long-run return and the largest drops. You might model 6% to 8%, but some decades deliver far less.
A cautious approach is to plan with the lower rate and treat anything above it as a bonus. If the 4% result meets your goal, you are in good shape. If only the 8% result does, you are relying on markets cooperating.
Remember that the steady returns in these tables are a simplification. Real portfolios go up and down, and the order matters: a large drop in year 28, when your balance is biggest, hurts more than the same drop in year 3.
Fees and taxes
Every percentage point of annual fees comes straight off your return. Moving from the 6% column to the 4% column is roughly what 2% in combined yearly fees would do. The investment fees guide shows how even 1% adds up over 30 years.
Taxes matter too. Tax-advantaged accounts, such as a 401(k) or IRA in the US, an ISA or pension in the UK, a TFSA or RRSP in Canada, or superannuation in Australia, can let more of the growth compound. Each has its own rules and annual limits, so check the current limit with your tax authority before you plan around one.
Frequently asked questions
Can $500 a month make you a millionaire?
At a steady 8%, $500 a month passes $1 million after about 33.4 years. At 6% it takes about 40.1 years, and at 4% about 51.1 years. Raising your deposits over time shortens those timelines considerably.
Does it matter if I invest at the start or end of the month?
A little. Investing at the start of each month at 6% for 30 years gives $504,769 instead of $502,258, a difference of $2,511, because each deposit gets one extra month of growth.
What if the market falls right after I start?
Early drops matter less than late ones, because your balance is small and each new $500 buys in at lower prices. A large fall near the end of your timeline does more damage, which is why many people shift toward lower-risk holdings as their goal gets close.
How much do I need to save each month to hit a specific number?
Work backward from the target. The savings goal calculator gives the monthly amount for any goal and date, and our guide on how much to save each month covers how to pick the target.
Next steps
- Decide what the money is for and when you'll need it. Under about five years, favor savings accounts and CDs over stocks.
- Pick a conservative planning rate, such as 4% for a mixed portfolio, and see whether $500 a month gets you where you want to be.
- Automate the deposit for the day after payday so it happens before you can spend it.
- Set a yearly reminder to raise the amount, even by $15 or $25.
- Check your total fees and use a tax-advantaged account if you're eligible.
Then plug your own numbers into the compound interest calculator and compare a 25-year and a 30-year timeline. Seeing the gap in dollars is often the push needed to start this month rather than next year.
This article is for general education and is not financial advice. Rules, rates and products vary by lender and country. See our disclaimer.
