Which tables and rules each calculator runs on, why we default to the assumptions we do, and what happens when a figure turns out wrong.
A retirement calculator is a stack of assumptions wearing a clean interface. This page lists the ones ours make: the IRS contribution and distribution rules built into specific tools, the growth and inflation defaults we picked and why, the research behind the 4% rule, and how often each of these gets rechecked.
Two of our tools have a hard dollar ceiling baked into federal law, and both are tax-year specific. The 401k calculator and 403b calculator use the IRS employee elective-deferral limit, $24,500 for 2026, plus an $8,000 catch-up for savers 50 and older and an enhanced $11,250 catch-up for savers aged 60 through 63 under the SECURE 2.0 Act's higher-catch-up provision. The Roth vs Traditional IRA calculator uses the IRA contribution limit, $7,500 for 2026 with a $1,100 catch-up at 50 and older, combined across all of a saver's IRAs, Roth and Traditional together. Both figures come from IRS Notice 2025-67, published Nov. 13, 2025. The IRS typically announces the following year's limits in its Revenue Procedure or Notice released each autumn; when a new figure is confirmed we update the calculator's placeholder value and label it with the tax year it applies to, rather than leaving a prior year's number sitting unmarked.
The RMD calculator runs on the IRS Uniform Lifetime Table from the life-expectancy regulations finalized in 2022 (Treasury Decision 9930), the table nearly all account owners use to divide their prior year-end balance by a life-expectancy factor and get the amount they must withdraw. Required distributions currently start at age 73 under the SECURE 2.0 Act; that start age is scheduled to rise to 75 in 2033. If you inherited the account rather than owning it outright, a different table and different timing rules can apply, and our calculator is built for the owner case, not the inherited-account case.
Where a calculator asks for an expected return, the placeholder is 6% a year. That sits below the long-run nominal average for a stock-heavy portfolio and above a bond-heavy one, on purpose, since it's a placeholder meant to be overwritten with your own assumption, not a forecast. Inflation defaults to 3%, close to the long-run average annual change in the Consumer Price Index and a notch above the Federal Reserve's 2% target, which gives withdrawal projections a small margin rather than assuming inflation stays permanently at target. Neither figure is a prediction. Markets have run well above and well below 6% for stretches of a decade or longer, and a retiree who plugs in a single average return misses the effect of a bad sequence of years early in retirement, sometimes called sequence-of-returns risk.
The 4% rule guide and the withdrawal-rate logic inside the savings withdrawal calculator trace to two pieces of research, not one. Financial planner William Bengen published the original analysis in 1994, testing withdrawal rates against historical U.S. stock and bond returns. Three finance professors at Trinity University, Philip Cooley, Carl Hubbard and Daniel Walz, extended that work in a 1998 paper that became known as the Trinity study, testing a range of withdrawal rates and stock-bond mixes against overlapping 30-year periods back to 1926. A 4% starting withdrawal, adjusted for inflation each year after, held up in the large majority of those historical periods for a 30-year horizon. It did not hold up in all of them, and both papers say so directly: the study is a look backward at U.S. market history, not a guarantee, and a retirement that runs longer than 30 years, or starts with a stretch of poor returns, is exactly the scenario where a fixed 4% comes under the most strain. Our guide page covers those limits and the flexible-withdrawal alternatives some retirees use instead.
The savings-by-age guide reproduces published age-based savings benchmarks (for example, having roughly 1 times salary saved by 30 and 10 times by 67) from Fidelity's retirement research, cited on that page with the year the figures were published. These are round guideposts from one large recordkeeper's data set, not a universal standard, and we say so on the page rather than presenting them as fact.
Contribution limits and the RMD start age are reviewed every year in the fourth quarter, after the IRS typically publishes the coming year's figures, and again in January once the new figures are in force. The RMD life-expectancy table itself changes far less often; we recheck it whenever Treasury issues new final regulations. Guide pages that cite a specific year's limit say so in the text rather than presenting a number as permanent, so a reader in 2027 reading about the 2025 limit can tell the difference at a glance.
If a calculator's default value no longer matches the current IRS or SSA figure, or a guide states a benchmark you can show is outdated, the fastest way to reach us is the contact page. We check the claim against the primary source, generally within the week, and update the page with the correct figure and the year it applies to. We do not silently edit a wrong number without a trace; if a page's guidance changed because a rule changed, that is worth knowing.
RetirementCalc is free to use and supported by display advertising and a small number of affiliate links; if you click through and buy something, we may earn a commission at no cost to you. That revenue has no bearing on which formula a calculator runs or what figure it returns. See the authors page for who writes and checks the material published here.