Resources · Boost
If I save an extra $500 a month, when can I retire?
Short answerSooner by real years. On typical numbers, an extra $500 a month pulls your Optional Date forward by 1 to 3 years. Earlier in your career, the pull is bigger, because the money has decades to compound.
“Retire” is what people search for. This page answers it as Work Optional. Below: a calculator, a worked example, and the formulas that show how much the boost is worth against your numbers.
Calculator
Try the boost against your numbers
Type in your numbers. Slide the extra amount and how long you can keep it up. The calculator shows the baseline Optional Date, the boosted Optional Date, and the exact pull-forward.
12%
Funded today
Years to Optional (boosted)
FEB 2045
vs baseline FEB 2047
Pull-forward: 24 months sooner
Extra per month
Keep it up for
Total extra contributed
$180K
Pull-forward
24 months sooner
Optional Target
$1.50M
A meaningful pull-forward. Optional lands more than a year sooner.
Assumes a 7% average real return (after inflation) and a 4% withdrawal rate.
Why $500 a month is worth more than $500 a month
The value of a monthly boost isn’t the boost itself. It’s what that money compounds into by the time you reach Optional. $500 a month at 7% real for 30 years lands at roughly $610,000 in today's dollars.
One assumption worth naming: the model treats the $500 as real. You bump the nominal amount with inflation over time to hold purchasing power. A frozen nominal $500/mo compounds to less than the number above.
The lever loses power the closer you are to Optional. Ten years out, a $500 monthly boost typically pulls the date forward by 12 to 18 months. Two years out, it's often less than 4 months. Compounding needs runway.
Worked example · illustrative
What a real boost does
Case study — Alex, 34 — illustrative case study, software engineer
Alex has $180,000 across his 401(k) and taxable brokerage. He saves $1,500 a month and spends about $60,000 a year. His employer just raised his salary, and he's wondering whether the extra $500 a month is worth investing or spending. Everyone tells him the difference is small.
Balance
$180,000
Monthly save
$1,500
Annual spend
$60,000
Boost
+$500/mo
Baseline: Optional lands about 23 years from now, at age 57. He's roughly 12% funded today ($180K against a $1.5M target).
Boosted to $2,000/mo for 30 years: Optional lands about 20 years from now. Roughly 3 years sooner. Total extra contributed: $180,000. Value at Optional: much larger, because it compounded the whole way.
Boost stops after 5 years: the pull-forward shrinks to about 15 months. Decades of consistency bend the curve, not the size of any one raise.
Inside the app
This decision, inside Project Optional
The same math runs in the Scenarios Lab. Sign in, type your numbers once, turn on the Boost lever, and compare the boosted Optional Date against your default plan.
The math
Assumptions and formulas
Same engine as the rest of the app.
Optional Number = Annual Spending ÷ 4% = Annual Spending × 25
Each month steps forward. Your balance grows at the monthly return, then adds your normal contribution plus the boost:
ending balance = starting balance × (1 + monthly return)
+ monthly contribution + boost
monthly return = (1 + 7%)^(1÷12) − 1 ≈ 0.565%/month
- 7% real (inflation-adjusted) return. Your target stays flat in today's dollars, so inflation isn't double-counted.
- Contributions and boost are in real (today's dollar) terms. The nominal amount tracks inflation; a frozen nominal contribution would compound to less.
- 4% safe withdrawal rate, from the Trinity Study. Fixed on this page; adjustable in the app.
- The boost is a real monthly addition, not a one-time bump. If it stops, the delay-reduction stops with it.
- No taxes on withdrawals or contributions. The 401(k) / Roth / brokerage choice matters in real life; it isn't modeled here.
- No Social Security. Every projection assumes zero government income once you stop working.
FAQ
What people ask about this
Is $100 or $250 a month worth it? Yes. Any amount that compounds for a couple of decades pulls the date forward. A $250 boost held for 30 years typically brings Optional 12 to 20 months closer.
What if I have to stop the boost after a few years? The pull-forward is much smaller. A five-year boost is still worth doing, but the impact is months, not years. Use the “keep it up for” chip in the calculator to see the difference.
Should I boost my 401(k) or my brokerage? On the math on this page, either. Both grow at 7% real. In real life the answer depends on your employer match (huge if there is one and you're leaving it on the table), your current marginal tax rate versus your expected withdrawal-era rate, whether you need the money before 59½, and whether you're using Traditional or Roth. An uncaptured match is almost always the first fix; the tax-rate comparison is the second.
Keep reading
Should I quit my high-paying job? →
The opposite lever, cutting income instead of adding to it. Same compounding math, running the other direction.
Can I afford a sabbatical? →
A useful place to spend the buffer a boost buys: twelve months off, without pulling from the portfolio.
Can I work part-time after Optional? →
The accumulation-side lever is on this page. Part-time income is the same trick applied later.
Membership
Save this boost and see it next to your real plan
Enter your numbers, turn on the Boost lever, and stack it against sabbaticals, layoffs, and every other scenario in the Lab.