Use this calendar calculation when dates follow the stated calendar and you need a reproducible boundary, interval, ordinal, week, or classification result.

Birth date

Birth date.

As of

Reference date for the calculation.

Compute completed years, months, and days between a birth date and a reference date. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Years (years)

Completed years.

Months (months)

Whole months beyond the years.

Days (days)

Whole days beyond the months.

• Calendar dates are not elapsed-time instants by themselves. Time zones, daylight-saving transitions, locale-specific week rules, inclusive endpoints, holidays, historical calendar reforms, and proleptic-calendar assumptions can change an apparently simple result.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Store instants with an explicit time zone when time of day matters, and document whether interval endpoints are inclusive. Supply a jurisdiction-specific holiday calendar for business-day decisions.

• Business Days Between Dates Calculator

  Count weekdays Monday through Friday in an inclusive date range, optionally subtracting supplied holidays.

• Business Days Between

  Count weekdays in a half-open date range, optionally subtracting supplied holidays.

• Date Difference Calculator

  Calculate the signed number of calendar days between two ISO dates.