Calculation methodology

All calculators run in the browser. They use integer minutes or whole calendar days as their calculation units, keeping rounding out of the underlying results.

Clock times and durations

The hours calculator accepts a start and end clock time. An earlier end is treated as tomorrow. An explicit next-day option also allows equal times to mean 24 hours. Breaks must be whole minutes and cannot exceed the full duration. Time zones and daylight saving are not applied.

The time calculator combines signed durations. Its hours field is not limited to 24. Each entry permits 0–999,999 hours and 0–59 minutes; there may be at most 50 entries. Decimal hour displays are rounded to four decimal places, while integer minutes are retained.

Calendar dates

Dates are validated in the Gregorian calendar, for years 0100–9999. A leap year is divisible by 4, except a year divisible by 100 must also be divisible by 400. Thus 2000 is a leap year and 2100 is not.

Calendar dates are represented at UTC midnight to compare them without local daylight saving changes. The result describes calendar-day differences, not the actual hours between two local midnights. Inclusive counting adds one to the elapsed-day result.

Age and month-end handling

The age calculator finds the largest number of complete months from the original birth date whose anniversary is no later than the end date. If a month lacks the original day, that anniversary is clamped to its last day. Each anniversary is anchored to the original date rather than calculated by repeatedly adding one month. Remaining days follow that last anniversary.

This convention produces January 31 to February 28, 2025 = 1 month, and February 29, 2020 to February 28, 2021 = 1 year. It is a stated calculation convention, not a legal rule.

Validation and corrections

Inputs are checked for valid dates, whole minutes, field ranges, and chronological order. Invalid combinations produce an error rather than a misleading result. Testing covers overnight shifts, equal dates, leap years, month ends, and negative duration totals.

If you report an issue, include the calculator name, example inputs, actual result, and expected result. Use fictional dates when possible rather than sending a real date of birth.