How Our Calculators Work

How a number reaches a calculator

A retirement calculator is only as good as the figures behind it, and those figures change every year. Our approach is to keep the path from agency page to on-screen result short and visible.

1. Find it on the agency's own page Premiums come from CMS and Medicare.gov, benefit amounts and earnings limits from the Social Security Administration, tax thresholds from IRS revenue procedures and forms, and Medicaid standards from CMS guidance. Blogs, news summaries and other calculators are leads to check, never sources.
2. Record it with its evidence Headline figures live in one data file, not scattered through page text. Each entry stores the value, the year it applies to, the date it takes effect, the link to the agency page, the sentence we relied on, and the date we last checked it.
3. Calculate from that record Tools read the stored figure rather than carrying their own copy. When a rule is shared by several tools, such as how a Social Security benefit shrinks when claimed early, it is coded once and reused.
4. Check before it ships Automated tests compare calculator output with worked examples published by the agencies, flag figures marked as not yet confirmed, and search the site for values left over from a previous year.

What a stored figure looks like

Here is one real entry, the 2026 Medicare Part B standard premium, shown the way it is kept. Anyone can follow the link and read the same sentence.

The Sources page lists every document these records point to.

Rules, rounding and a worked example

Getting the formula right is not enough if the rounding is wrong, because retirement benefits are paid in whole dollars. Where an agency publishes a rounding rule, the calculator follows it. For Social Security, the primary insurance amount is rounded down to the next dime and the monthly benefit is rounded down to the next dollar.

Claiming early, step by step

SSA reduces a retirement benefit by 5/9 of 1% for each month claimed before full retirement age, up to 36 months, and by 5/12 of 1% for each month beyond that. Someone who claims 60 months early is reduced by 20% for the first 36 months plus 10% for the next 24, for a total of 30%. Our early-claiming results are built from that arithmetic, and the tests check it against SSA's published figures.

Medicare surcharges look back two years

The income-related monthly adjustment amount (IRMAA) is based on the tax return from two years earlier, so 2026 premiums use 2024 income. If a life-changing event has lowered your income since then, SSA lets you ask for a new determination using Form SSA-44.

Keeping figures current

Agencies publish new amounts on their own schedule: SSA announces the cost-of-living adjustment in October, CMS releases next year's Medicare premiums in the fall, and the IRS publishes inflation adjustments for the coming tax year in the autumn. When new figures appear we add them as new records rather than overwriting the old ones, so a tool can offer both years. The Social Security benefits, earnings test and RMD calculators already let you choose between 2026 and 2027.

Some agency pages lag behind the announcement. When an agency's detail pages still show last year's amounts, we use the announcement and record the gap in our own notes instead of guessing.

What happens to what you type

Calculations run in your browser. The income, ages and balances you enter are not sent to our servers. Our privacy policy explains this in full, including how you can confirm it with your browser's network tab.

What an estimate cannot see

• Your actual records. SSA computes benefits from your real earnings history. A calculator uses the numbers you give it. Your my Social Security account shows the record SSA holds.
• Your full tax return. Our tax tools estimate federal effects of the income you enter. Credits, state rules and unusual income can change the real answer, and each tool says what it leaves out.
• Individual decisions. Agencies decide eligibility and amounts case by case. If a result here and an agency notice disagree, the notice controls.
• Advice. These are education tools. For divorce, estate, disputes with the IRS or major withdrawal decisions, a qualified professional can look at your whole situation.

If a number looks wrong

Send us the page, what you entered, and the agency page you are comparing against, using the contact page. We check the source ourselves and correct the tool or page if the source supports you. Mistakes in government figures are rare but real, and readers who compare against the source are how we catch ours.