About Retire By When

Retire By When is eight retirement calculators built around one idea: show the formula, not just the number. Every tool states the math it runs, works a real example through to the penny, and cites the IRS figure or published rule of thumb it relies on -- the current 401(k) contribution limit, the IRS Uniform Lifetime Table for required minimum distributions, the origin of the 4% rule.

How the calculators work

Every growth projection on this site -- 401(k), Roth IRA, traditional IRA, the retirement savings target -- runs through one shared engine that simulates month by month, rather than a single end-of-horizon formula. Where a textbook closed-form formula applies exactly (a flat contribution, a whole number of years), that formula is used as an independent cross-check in the site's own test suite, so the simulation and the textbook math are proven to agree to the cent before anything ships.

Where the IRS figures come from

2026 contribution limits (401(k) elective deferral, IRA contributions, and the age-50 and age-60-63 catch-ups) come from IRS Notice 2025-67. Required minimum distribution divisors come from IRS Publication 590-B, Appendix B, Table III (the Uniform Lifetime Table). Both are linked directly from the pages that use them, not just named. Net worth reference figures come from the Federal Reserve's own Survey of Consumer Finances, labeled clearly as Federal Reserve data rather than this site's own numbers.

What it doesn't do

This isn't financial, tax or legal advice, and Retire By When isn't affiliated with any employer, plan administrator, bank, brokerage or the IRS. Every result is an estimate built from constant-rate, constant-contribution assumptions -- real accounts have fees, variable returns, plan-specific rules and tax situations this tool can't know. See Terms.

Every calculator

• 401(k) Calculator -- Project your 401(k) balance at retirement from salary, contribution rate, employer match and return, with the current IRS elective-deferral limit applied.
• Roth IRA Calculator -- Roth IRA growth at your contribution, years and return, with the IRS limit and 50+ catch-up shown, compared to a taxable account at your marginal rate.
• Traditional IRA Calculator -- Traditional IRA growth on a deductible contribution, tax-deferred until withdrawal, with the tax bill at your stated withdrawal tax rate shown separately.
• Retirement Savings Calculator -- Check your projected retirement balance against a spending target using the 4% rule or your own rate, with the gap and monthly savings needed to close it.
• Retirement Withdrawal Calculator -- How long a retirement balance lasts at a given withdrawal rate, expected return and inflation, with a year-by-year table showing when it runs out.
• RMD Calculator -- Your required minimum distribution from a traditional IRA or 401(k), using the IRS Uniform Lifetime Table, with a multi-year projection of future RMDs.
• Net Worth Calculator -- Total assets minus liabilities by category, with a Federal Reserve reference table showing median net worth by age so you can see where you stand.
• Budget Calculator -- Split your take-home pay into needs, wants and savings using the 50/30/20 rule or your own percentages, with a monthly table.

Corrections

If a formula, IRS figure or citation here is wrong or out of date, email hello@retirebywhen.com.