Calculating contract durations, project timelines, and deadlines. Working out exactly how many workdays (Mon–Fri) fall between two dates for invoicing or project estimation. Verifying age cut-offs (visa eligibility, school years, milestone birthdays). Adding "30 days net" or "90 day cooling-off" periods to a baseline date in a way that handles month-end correctly.

Inclusive vs exclusive end dates. "Days from Mon to Fri" is 4 if you count gaps, 5 if you count days. The toggle controls which convention; both are right depending on the question. Add/subtract order matters. Years and months apply first, then weeks and days. Adding "1 month + 1 day" to Jan 30 gives Mar 1 (Feb 30 → Feb 28/29 → +1), not Mar 2 — which is the calendar-safe convention almost every datetime library uses. Workdays don't include holidays. The calculation knows weekends but not bank holidays — adjust manually if it matters. "Total months" is approximate in the age view (years × 12 + months) — it ignores the trailing days. The Y/M/D figure is exact. UTC anchoring trades off with locale. A date in your local timezone might map to a slightly different UTC day. For most uses (deadlines, ages) UTC noon is the safer anchor; for to-the-minute timezone work use the timezone converter.

Calculatrice de Dates

Jours entre deux dates · ajouter ou soustraire jours/semaines/mois/années · âge en années, mois et jours.

Mode

Vers

Include the end date in the count

Résultat

Saisissez une entrée ci-dessus pour voir le résultat.

What is this for?

Three things people actually want from a date calculator: the gap between two dates ("how many days until launch?"), shifting a date by a span ("90 days after invoice date"), and a precise age ("years, months, and days from a date of birth"). This tool does all three, in your browser, anchored to UTC noon so DST and timezone shifts don't quietly wrong the answer when you travel.

When to use it

Calculating contract durations, project timelines, and deadlines.
Working out exactly how many workdays (Mon–Fri) fall between two dates for invoicing or project estimation.
Verifying age cut-offs (visa eligibility, school years, milestone birthdays).
Adding "30 days net" or "90 day cooling-off" periods to a baseline date in a way that handles month-end correctly.

Common gotchas

Inclusive vs exclusive end dates. "Days from Mon to Fri" is 4 if you count gaps, 5 if you count days. The toggle controls which convention; both are right depending on the question.
Add/subtract order matters. Years and months apply first, then weeks and days. Adding "1 month + 1 day" to Jan 30 gives Mar 1 (Feb 30 → Feb 28/29 → +1), not Mar 2 — which is the calendar-safe convention almost every datetime library uses.
Workdays don't include holidays. The calculation knows weekends but not bank holidays — adjust manually if it matters.
"Total months" is approximate in the age view (years × 12 + months) — it ignores the trailing days. The Y/M/D figure is exact.
UTC anchoring trades off with locale. A date in your local timezone might map to a slightly different UTC day. For most uses (deadlines, ages) UTC noon is the safer anchor; for to-the-minute timezone work use the timezone converter.