Methodology

One tested calculation engine

Every calculator on DayCentsruns on a single, shared calculation engine rather than one-off formulas scattered across pages. Money is computed in exact integer cents to avoid rounding drift, and each function is covered by automated tests — including "golden" tests that check our output against authoritative references such as spreadsheet functions (PMT, FV, PV), published amortization tables, and worked examples from the IRS.

How we handle official data

Anything that changes by law or by year — federal tax brackets, standard deductions, FICA rates, retirement contribution limits — comes from typed datasets sourced directly from primary documents (IRS Revenue Procedures and Notices, the Social Security Administration). Each dataset records its source, publication date, and the date we last verified it. Every calculator that depends on one shows those details, with a link to the primary document, in the “Sources” section of its page. Calculators that use no external data say so in the same place rather than leaving it blank — most of our tools are pure arithmetic, and pure arithmetic has nothing to cite beyond its formula.

When the law changes, we update the underlying dataset once and every dependent calculator updates with it — so a paycheck tool and a retirement tool never disagree about the same year's rules.

Assumptions are always visible

Calculators are models, and every model makes assumptions. We state them plainly on each tool: the compounding frequency, whether figures are before or after tax, what a rate includes, and what the tool does not account for. Results are educational estimates based on the inputs and stated assumptions — not quotes, offers, or personalized advice.

Comparisons and rankings

We do not currently rank or compare financial products: there are no rate tables, no "best of" lists, and no partner offers on the site. If we add them, the scoring rubric will be published on this page before the first comparison goes live, paid placements will be visually distinct and labeled, and neither will ever alter a calculator result.

Corrections

If you find an error in a calculation or a data point, please tell us via the contact details on our About page. We investigate promptly and correct transparently.