How the projection works
The calculator grows your current savings and each monthly contribution with compound interest until your retirement age. Returns are compounded monthly at one twelfth of the yearly rate, and contributions are added at the end of each month.
Future value = P × (1 + i)n + M × ((1 + i)n − 1) ÷ i
where i = yearly return ÷ 12 and n = years × 12
Then it divides the result by the growth of prices over the same years to show the value in today's money, which is what really tells you how comfortable retirement will be.
Worked examples
| Start | Monthly | Return | Years | You put in | Projected balance |
|---|---|---|---|---|---|
| 10,000 | 500 | 6% | 30 | 190,000 | 562,483 |
| 50,000 | 1,000 | 5% | 20 | 290,000 | 546,666 |
| 0 | 300 | 7% | 40 | 144,000 | 787,444 |
| 100,000 | 0 | 5% | 10 | 100,000 | 164,701 |
The third row shows the power of starting early: 300 a month for 40 years beats 1,000 a month for 20 years, even though the total paid in is less than half. In the first example, 562,483 in 30 years is worth about 268,160 in today's money if prices rise 2.5% a year.
The 4% rule
A common rule of thumb says you can withdraw about 4% of your savings in the first year of retirement, then increase the amount with inflation, and have a high chance of the money lasting 30 years. It comes from US research on historical stock and bond returns (the "Trinity study" and William Bengen's work in the 1990s).
| Savings at retirement | 4% per year | Per month |
|---|---|---|
| 164,701 | 6,588 | 549 |
| 546,666 | 21,867 | 1,822 |
| 562,483 | 22,499 | 1,875 |
| 787,444 | 31,498 | 2,625 |
Treat 4% as a starting point, not a guarantee. Retiring early, retiring into a market crash or living in a country with different returns may call for 3–3.5%; a flexible spending plan or a pension can allow more.
Choosing realistic inputs
- Return: long-run nominal returns for diversified portfolios are often assumed at 4–7% a year; cash savings earn less. Subtract fund fees, which can be 0.1% to over 1% a year.
- Inflation: many central banks target about 2%; 2.5–3% is a cautious assumption.
- Real return: return and inflation combine as (1 + return) ÷ (1 + inflation) − 1. A 6% return with 2.5% inflation is a real return of about 3.41% a year.
- Contributions: include employer contributions and tax relief, which can add a lot.
How much do I need?
A quick way to set a target: decide the yearly income you want from savings in today's money, subtract any state or company pension, and multiply the gap by 25 (the inverse of 4%). Needing 20,000 a year from savings means a target of about 500,000 in today's money. Many planners suggest aiming to replace about 70–80% of your pre-retirement income in total.
Ways to close a gap
- Start or increase contributions early; time does more work than the amount.
- Raise contributions with every pay rise, for example by half of the increase.
- Keep costs low; a 1% yearly fee can take a large share of the final balance over 30 years.
- Work a little longer; each extra year adds contributions and growth and shortens the period the money must last.
Limits of this calculator
Returns are never smooth: real portfolios rise and fall, and the order of good and bad years matters near retirement. The projection also ignores taxes, which differ by country and account type. Use it to compare scenarios, and review your plan every year or two.
This calculator is for general education, not financial advice. Consider speaking to a licensed financial adviser about your personal situation.
The cost of waiting and of fees
| Scenario (500 a month) | Projected balance | Difference |
|---|---|---|
| Start at 35, 6% a year, 30 years | 502,258 | – |
| Start at 40 instead, 25 years | 346,497 | about 31% less |
| Default example (10,000 start) at 6% | 562,483 | – |
| Same, but a 1% yearly fee (5% net) | 460,807 | about 18% less |
Five years of delay cost almost a third of the final balance, even though only 30,000 fewer is paid in. A 1% fee looks small each year but compounds against you for decades. Both are easy to check by changing the inputs above.
Frequently asked questions
How much will I have if I save 500 a month for 30 years?
Starting from 10,000 at a 6% yearly return, about 562,000, of which 190,000 is what you paid in. In today's money, with 2.5% inflation, that is about 268,000.
What is the 4% rule?
A rule of thumb that withdrawing about 4% of your savings in the first year of retirement, then adjusting for inflation, has historically lasted around 30 years.
How much do I need to retire?
Multiply the yearly income you need from savings by 25. For 20,000 a year, that is about 500,000 in today's money.
What return should I assume?
Many planners use 4–7% a year before inflation for a diversified portfolio, minus fees. Use a lower figure for cash or very cautious investments.
How much does starting 5 years later cost?
Saving 500 a month at 6%, starting at 40 instead of 35 leaves about 346,000 instead of 502,000 at 65, roughly 31% less.
Sources
- Bengen WP. Determining Withdrawal Rates Using Historical Data. Journal of Financial Planning, 1994.
- Cooley PL, Hubbard CM, Walz DT. Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable (Trinity study). AAII Journal, 1998.
- Investor.gov (U.S. SEC), Compound interest calculator and retirement planning resources.
Last reviewed 7 October 2026. Results are estimates; see our disclaimer.