Methodology: how we build and check our tools

Every TimeTally tool follows the same process so you can trust the answer — and check it yourself.

1. Recognized formulas and sources

Formulas come from published, widely accepted sources. The main ones used on this site are:

• Gregorian calendar leap-year rules and ISO 8601 week numbering
• The IANA time zone database (used by your browser) for world time and daylight saving
• US Social Security Administration full retirement age schedule
• Registry RDAP records for domain registration dates
• Pew Research Center generation ranges

2. Tested against worked examples

Before a tool goes live, it is run with the example inputs shown on its page and the result is compared with a hand-checked answer. Edge cases — zero, very large numbers, leap years, empty fields — are tested too, and the tool shows a clear message instead of a wrong number.

3. Shown on every page

Each page has a How it works section, the formula and a worked example, so you can repeat the calculation by hand.

4. Rounding

Calculations use full precision internally. Results are rounded only for display — money to cents, most measurements to 2–4 decimal places.

5. Limits

Tools give estimates for general information. They cannot know your full situation. For money, health, legal or tax decisions, confirm with a qualified professional.

6. Updates and corrections

Rates and tables that change (such as tax brackets) are reviewed at least once a year. If you think a result is wrong, please tell us — we check every report.