Savings Rate and Years-to-FI Calculator

The formula

annual savings = take-home income − annual expenses
savings rate   = annual savings ÷ take-home income × 100
FI number      = annual expenses ÷ (withdrawal rate ÷ 100)

balance = current invested net worth
year    = 0
while balance < FI number and year < 80:
    balance = balance × (1 + real return ÷ 100) + annual savings
    year    = year + 1

Every rate above is a percentage rather than a fraction, which is why each one is divided by 100 before it is used: a 5% real return multiplies the balance by 1.05, and a 4% withdrawal rate divides spending by 0.04.

Savings are added at the end of each year, so a year's contribution earns nothing in the year it is made. That is the conservative ordering. The count stops the first year the balance reaches the FI number, and the year you get there is simply this calendar year plus that count.

If eighty years pass without the balance arriving, we say so instead of printing a number, because at that point the honest answer is "not on this trajectory". The same is true when spending is at or above income and the portfolio has not arrived yet: nothing is going in, so there is no timeline to project. The one case that is checked before either of those is a balance that already covers the FI number, because then the answer is "now" no matter what is going in or out each year.

A balance that already covers the number has no run-up left to chart, so the chart carries the same recurrence ten years forward instead. That line does not always point up: if you spend more than you take home and the draw is bigger than the balance earns, it points down, and it can cross back under the FI number. The verdict is written from that line rather than from the sign of the yearly flow, which is why being at your number reads three different ways here, and why drawing more than the portfolio earns is not called the same thing as still adding to it.

Why the savings rate is the whole story

The share of your income you keep does two jobs at once. It sets how much goes into the portfolio every year, and it sets how big that portfolio has to get, because the portfolio only ever has to cover what you actually spend. Cut a dollar from your annual spending and both happen together: a dollar more goes in each year, and the target itself drops (by twenty-five dollars at a 4% withdrawal rate, by about thirty-three at 3%).

That is why the timeline falls away so quickly as the rate climbs, and why a raise on its own moves it far less than people expect. Starting from nothing invested, income cancels out of the arithmetic completely: at a 50% savings rate the answer is exactly the same number of years whether you take home $50,000 or $500,000, because both the amount going in and the amount needed scale together. The table above is that fact, laid out.

Reading the reference table

Each row asks a single question: if you saved that share of the same take-home income and lived on the rest, how long would it take? Spending, the FI number and the annual contribution are all recomputed for the row, starting from the invested balance you entered, so the whole table is about your situation rather than a generic one. Your own rate is highlighted, and inserted in order if it does not land on one of the round numbers. Rates are shown to one decimal place, so a rate that rounds all the way to 0% or 100% gets no row: the label would contradict the spending and the contribution printed beside it.

What this does not account for

• Income and spending that change. Both are held flat for the whole projection. Raises, career breaks, children, and moving house all move the line, usually more than the return assumption does.
• Taxes. Income here is take-home, so tax on the way in is already handled. Tax on the way out is not: money coming from traditional accounts is taxable income when you withdraw it, so the portfolio has to be larger than this to fund the same spending.
• Getting at the money before 59½. Reaching the number is one problem, reaching the balances is another. The Roth conversion ladder calculator covers the bridge years.
• The order returns arrive in. A steady real return smooths over the fact that a poor first decade and a strong one produce very different results from the same average. The safe withdrawal rate explorer shows what the historical record looks like.
• Anything besides the portfolio. Social Security, a pension, part-time income, or a paid-off house all change what the portfolio has to carry. See the Lean, Fat and Barista FIRE calculator for the part-time case.

Shared assumptions

• Returns are real, not nominal. Every return figure on this page is already inflation-adjusted, so all dollar amounts are in today's money. There is no separate inflation input to set.
• Returns are smooth. The same return is applied every year. Real markets are not smooth, and the order in which good and bad years arrive changes outcomes materially.
• No taxes, fees, or lumpy spending. Investment fees, taxes on withdrawals, one-off costs, and changes in your spending over time are not modelled.
• Nothing leaves your browser. The whole calculation runs client-side. We do not receive, log, or store anything you type.