How the retirement calculator works
This calculator works in two stages. First, it projects your balance at retirement by simulating your savings growing one year at a time from your current age to your retirement age: each year, your balance grows by your expected pre-retirement return, and your annual contribution is added on top. This is the same style of year-by-year simulation used in our FIRE calculator, just run for a fixed number of years instead of solved for.
Second, it checks whether that balance actually lasts through retirement: starting from your projected balance, each year your balance grows by your (typically more conservative) post-retirement return, and your desired annual income is withdrawn. The calculator counts how many years this lasts before the balance would go to zero — if it crosses zero before your life expectancy, that age is your projected "runs out" point. This is a deliberately simple projection — no Monte Carlo simulation of variable market returns, no tax modeling, and no Social Security or pension income are included.
This calculator answers a different question than a FIRE calculator. A FIRE calculator solves for how many years it takes to reach a target portfolio, treating your retirement age as an output. This calculator instead takes your retirement age and desired spending as fixed inputs, and checks whether that specific plan actually survives — a check on a plan you've already chosen, rather than a search for when you could stop working.
Worked example
Suppose you're 35 years old with $30,000 saved, adding $10,000 a year, expecting a 7% annual return until you retire at 65.
Simulating 30 years of growth and contributions gives a projected balance at retirement of $1,172,976.
Now suppose you want $90,000 a year in retirement income, and expect a more conservative 5% return once retired, planning to age 90. Simulating withdrawals against that balance shows it's projected to run out at age 87 — three years short of age 90 — leaving a balance of $0 at life expectancy instead of a cushion. This plan, as entered, comes up short: something has to change (saving more, spending less in retirement, or retiring later) to close that three-year gap.
Common mistakes to avoid
1. Using the same return rate before and during retirement
Many people carry their pre-retirement, stock-heavy return assumption straight into retirement without adjusting for a more conservative post-retirement allocation. Using a lower return rate during retirement (as this calculator encourages) gives a more realistic, cautious projection.
2. Forgetting that "desired income" is on top of what you already withdraw from savings
The desired annual retirement income entered here is assumed to come entirely from the projected balance — it doesn't net out other income sources like Social Security, a pension, or part-time work. If you have other retirement income, your real "gap to fill" from savings is smaller than the figure you enter here.
3. Treating a "never runs out" result as guaranteed
This is a single fixed-rate projection, not a simulation across many possible market outcomes. A real retirement will experience some years of higher and lower returns, especially in the sequence that returns arrive (a downturn in the first few retirement years is far more damaging than one later on) — something this simplified model doesn't capture.