Retirement calculators that show their work

Retirematics is an independent publisher of free retirement calculators. Nine of them cover the decisions that come up between the last paycheck and the end of a long retirement — when to claim Social Security, how long the savings last, how to take money out of an IRA before 59½ without the penalty, whether to take the pension or the lump sum, and how far you are from not needing to save at all. Every rule a calculator applies is stated on its page and traced to the SSA or IRS document it came from.

• Social Security break-even calculator

  Benefit at any claiming age from 62 to 70 for your birth year, the break-even age between two claims, with COLA and an investment-return option, and the spousal benefit.

• Taxable Social Security calculator

  How much of a benefit is taxable under IRC §86, figured line by line as Publication 915's worksheet does, the federal tax on it, and what one more $1,000 of income does while benefits are being pulled into income.

• Retirement withdrawal calculator

  How long savings last with spending that rises with inflation, Social Security and a pension starting on their own dates, and federal tax on withdrawals estimated with the 2026 brackets.

• RMD calculator

  Your required minimum distribution for the year from the IRS Uniform Lifetime or Joint and Last Survivor table, its deadline including the April 1 rule for the first year, the excise tax if it is missed, and a year-by-year projection.

• 72(t) SEPP calculator

  All three Notice 2022-6 methods side by side, every permitted life-expectancy table, the 5%-or-120%-AFR ceiling looked up from the actual revenue ruling for your start month, and the date the series may change.

• Safe withdrawal rate calculator

  Three ways to test a withdrawal: against every retirement since 1928 one starting year at a time, against 10,000 plans of years drawn at random from that record, or against one constant return. Names the start years that failed and the rate that never did.

• Pension vs lump sum calculator

  What the pension is worth today, the return the lump sum would have to earn to match it, and when a lump sum paying the same amounts would run out.

• Coast FIRE calculator

  The amount that, invested today, grows to your retirement number by the age you choose with no further contributions — and whether you are already there.

• FIRE calculator

  Your FI number and the years to reach it from your savings rate, with the table of every savings rate from 10% to 70%.

What is different about these

• The Social Security figures come from the SSA's own reduction and credit rules by month, not from a rounded table, and the break-even is computed month by month with the COLA applied each December.
• The 72(t) calculator uses the 2022 life-expectancy tables and mortality rates from Treas. Reg. §1.401(a)(9)-9, and the interest-rate ceiling is looked up from the monthly revenue rulings — the tool reproduces the IRS's own worked examples to the dollar.
• The RMD calculator uses the Joint and Last Survivor Table when the sole beneficiary is a spouse more than ten years younger, rather than assuming everyone is on the Uniform Lifetime Table, and it states the first year's April 1 deadline, the Roth exemption, the 2026 charitable-distribution limit and the applicable age for a 1959 birth, which the statute leaves described by two conflicting clauses. The divisors themselves are published with the percentage each works out to.
• The withdrawal calculator grosses each year's withdrawal up for federal income tax, including the taxable share of Social Security under IRC §86, instead of asking you to guess an effective rate; the taxable Social Security calculator shows that §86 arithmetic line by line, as Publication 915's worksheet lays it out.
• Everything runs in your browser. Nothing you type is stored or sent anywhere; "copy link" puts your inputs in the address so you can come back to them.

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