How are leap years handled?

Use the Feb 29 policy to decide common‑year celebrations: Mar 1, Feb 28, or nearest.

What does inclusive days mean?

It counts both the start and end dates, adding one day to the total.

It divides total days by a basis (e.g., 365.2425) with configurable rounding and decimals.

For date‑only math, usually no. Enable times to consider hour‑level precision.

Calendar years ignore month/day and report the absolute difference in birth years. Actual uses Y–M–D.

Date

Time (optional)

Date

Time (optional)

Timezone (applies to both) Basis

Decimal‑year divisor

Rounding

Decimals

Inclusive days

Use times

Feb 29 policy

Locale

Tip: Toggle Use times for hour‑level precision; leave off for pure calendar math.

Compare ages on date

Computes ages of A and B on this date and the gap then (Y–M–D and decimal).

Upload a CSV with two columns (A,B) in YYYY-MM-DD or YYYY-MM-DD HH:MM. We’ll compute decimal years and Y–M–D for each pair.

FAQ & Notes

Leap years: Feb 29 policy controls how anniversaries are treated in common years.
Inclusive days: Adds one day to the day count (e.g., 1 Jan to 2 Jan is 2 days).
Calendar vs Actual: Calendar years ignore month/day; Actual is full Y–M–D then totals.
Timezone: For most cases, local/UTC produce the same Y–M–D; toggle "Use times" when hour‑level precision matters.
Privacy: All calculations happen in your browser. The API endpoint is optional.