Methodology
How our numbers are worked out, and how we keep them current.
How calculator formulas work
Each calculator uses standard, published formulas, and every tool page shows the formula under "How this calculator works" with a worked example. Calculations run in your browser using the numbers you enter. Results are rounded for display, usually to the cent for money and to two decimal places for percentages. Intermediate steps use full precision.
How assumptions are chosen
When a calculation needs an assumption, we use the most common case and show it on the page so you can change it. Examples:
- A full-time year is 40 hours a week for 52 weeks (2,080 hours)
- Monthly pay is annual pay divided by 12, so it's an average
- Biweekly pay assumes 26 paychecks a year; semimonthly assumes 24
- Savings and debt tools assume steady rates and monthly payments
- Overtime defaults to time and a half for hours over 40 in a workweek, following the federal Fair Labor Standards Act
Tax-year data
Tax rules change every year. Our tax tools read from a single data file per tax year containing the standard deduction, federal income tax brackets, and Social Security and Medicare rates. Each tool shows which tax year it uses.
- Current data: tax year 2026
- Sources: the IRS announcement of 2026 inflation adjustments, and the Social Security Administration's contribution and benefit base
- Updates: when the IRS publishes the next year's figures, typically in the fall, we add a new data file and review the tools that use it
Our tax estimates are simplified. They don't include credits, itemized deductions, or every special rule. They are not official IRS calculations.
How information is reviewed
Before publishing, each calculator is tested against hand-worked examples, including edge cases like zero values and invalid entries. Guides are checked against their sources, and dates are shown on every article. When a source changes, we update the page and its "updated" date.
Sources we prefer
For rules and figures that change, we rely on primary sources such as the IRS, the U.S. Department of Labor, the Social Security Administration, the Bureau of Labor Statistics, the Census Bureau, and official state websites. We link to them where they're used. We don't invent statistics or citations.
Estimates may differ from actual results
Your real paycheck, loan balance, or investment return can differ from our estimate because of rounding, timing, fees, or rules specific to your situation. See the disclaimer.
Found an error?
Please let us know. Corrections are welcome and taken seriously.