Retire-at-X Calculator.
Forecast your retirement balance at any target age and see whether it covers your annual expenses at a safe withdrawal rate — the Trinity Study 4% rule made concrete.
Before you run the numbers.
Most retirement calculators ask "how much do I need?" and stop there. This one asks a more useful question: at the age you're actually planning to retire, with the balance and contribution rate you actually have today, does the math work?
Enter your current age, target retirement age, current balance, and monthly contribution, plus a return assumption for the years before and after retirement. The calculator projects your balance forward using standard compound-interest math, then checks that projected balance against your estimated retirement spending using a safe withdrawal rate — 4% is the Trinity Study benchmark, the same research that underlies the FIRE movement's "25x annual expenses" rule of thumb.
If the projection falls short, the calculator back-solves the monthly contribution that would close the gap — so instead of a vague "save more," you get a specific number to work toward. This is the same math every retirement-planning book from The Simple Path to Wealth to Your Money or Your Life is built on, run against your own numbers instead of a generic example.
Run your scenario.
Historical S&P 500 long-run real return ~7% (FRED). Past returns don't guarantee future results.
More conservative due to bond-heavy allocation in retirement. Typical range: 3%–5%.
4% is the Trinity Study benchmark — assumes a 30-year retirement + ~60/40 stock/bond allocation.
See a worked example
Age 35, targeting retirement at 65, starting with $50,000 and contributing $1,000/month at an assumed 7% annual return.
FV = P(1+r)n + PMT · [((1+r)n − 1) / r], r = 0.07/12, n = 30×12
FV ≈ $1,625,796 at age 65
At a 4% safe withdrawal rate, that balance supports ~$65,032/year — more than the $60,000 assumed annual expenses, so this scenario reads on track.
Educational tool, not financial advice. Projection only — actual returns vary and past returns don't guarantee future results. The 4% rule (Trinity Study) assumes a 30-year retirement and a ~60/40 stock/bond allocation. This ignores taxes and Social Security. Consult a licensed financial professional before making retirement decisions.
Taught in these books.
Common questions.
Why does the return assumption change before and after retirement?
Most retirement plans shift toward a more conservative, bond-heavy allocation once you start drawing down the portfolio, to reduce the risk of a bad sequence of returns early in retirement. This calculator lets you set a higher pre-retirement return (typically equity-heavy, ~7% real historically) and a lower post-retirement return (typically 3-5%) to reflect that shift.
What is the safe withdrawal rate (SWR) and why default to 4%?
The SWR is the percentage of your portfolio you withdraw in year one of retirement (adjusted for inflation in subsequent years) without running out of money over a typical 30-year retirement. William Bengen's 1994 research and the later Trinity Study both converged on ~4% as sustainable across most historical 30-year windows for a 60/40 stock/bond portfolio. Longer retirements or more conservative planners often use 3-3.5% instead.
What does "way behind" vs. "behind" mean?
Both mean your current contribution rate won't reach your target by your chosen retirement age. "Behind" means the required monthly contribution to close the gap is less than double your current contribution — a stretch but plausible. "Way behind" means it's more than double, signaling you likely need to adjust your retirement age, spending target, or savings rate rather than just contribute a bit more.