Short answer: starting from zero, the share of your take-home pay you save largely decides how long it takes to reach financial independence, whatever you earn. At a 5% return after inflation and a 4% withdrawal rate, saving 10% takes about 51 years, 25% about 32, 50% about 17 and 70% about 9. A higher savings rate works twice: you invest more each year, and you need a smaller portfolio because you’ve learned to live on less.
Why income drops out of the math
Call your take-home pay P and your savings rate s. You invest s × P a year and spend (1 − s) × P. At a 4% withdrawal rate your FIRE number is 25 times spending, or 25 × (1 − s) × P. Both the yearly saving and the target are proportional to P, so for someone starting from zero, P cancels: a household on $50,000 and one on $200,000 that both save 40% need the same number of years. (Existing savings, and spending that changes in retirement, break this symmetry; the calculator handles both.)
The number of years n is the solution of s × P × ((1 + r)n − 1) ÷ r = (1 − s) × P ÷ w, where r is the real return and w the withdrawal rate. Rearranged: n = ln(1 + r × (1 − s) ÷ (s × w)) ÷ ln(1 + r).
Years to financial independence by savings rate
| Savings rate | Target (× take-home pay) | Years at 3% real | Years at 5% real | Years at 7% real |
|---|---|---|---|---|
| 10% | 22.5× | 69.3 | 51.4 | 41.7 |
| 15% | 21.3× | 56.1 | 42.8 | 35.3 |
| 20% | 20.0× | 46.9 | 36.7 | 30.7 |
| 25% | 18.8× | 39.9 | 31.9 | 27.1 |
| 30% | 17.5× | 34.2 | 28.0 | 24.0 |
| 40% | 15.0× | 25.5 | 21.6 | 19.0 |
| 50% | 12.5× | 18.9 | 16.6 | 15.0 |
| 60% | 10.0× | 13.7 | 12.4 | 11.4 |
| 70% | 7.5× | 9.4 | 8.8 | 8.3 |
| 80% | 5.0× | 5.8 | 5.6 | 5.4 |
Two patterns stand out. Each extra 10 points of savings rate saves the most time at the low end: going from 10% to 20% cuts about 15 years at 5% real, while 60% to 70% cuts under 4. And the return assumption matters less as the savings rate rises: at 70%, the gap between a 3% and a 7% real return is about a year, because most of the target comes from contributions, not growth.
A worked example
Sam takes home $70,000 and spends $52,500, a 25% savings rate. At a 4% withdrawal rate the target is $1,312,500 (25 × $52,500) and, at 5% real, it takes about 31.9 years. If Sam trims spending to $42,000, the savings rate rises to 40%: the target falls to $1,050,000, the yearly investment rises to $28,000, and the estimate drops to about 21.6 years. Cutting $10,500 a year of spending brings the date forward by roughly a decade in this example. Open Sam’s second scenario in the calculator and its savings-rate table updates for your own pay.
What the table leaves out
- Money you already have. Existing savings shorten every row; enter them in the calculator.
- Taxes. “Take-home pay” is after tax. Pre-tax 401(k) contributions never appear in take-home pay, so add them to both your pay and your savings when you work out your rate, and remember they’re taxed when withdrawn. The table doesn’t model taxes.
- Uneven returns and changing spending. Real returns vary every year, and retirement spending can differ from working spending (health insurance, for example). Treat the years as estimates.
- The withdrawal rate. At 3.5% instead of 4% every target is about 14% larger; see the 4% rule vs 3.5%.
Related reading: Lean FIRE vs Fat FIRE for choosing the spending level, and investment fees and your FIRE date for the other lever you control.
