Weeks Between Dates Calculator

It validates both dates as ISO 8601 calendar dates (YYYY-MM-DD), converts them to calendar day numbers, and subtracts those integers. Weeks come from days divided by 7. Using calendar day numbers instead of local clock instants prevents daylight saving transitions and time zones from shifting the count.

Calendar days count every date in the range, weekends included. Business days count Mondays through Fridays only, so one business week equals five business days. Toggle "Count business days only" to use that five-day week. Public holidays are not deducted here; use the business days calculator when holidays matter.

Both readings are valid and the right choice depends on what you are counting. Leave the end date out (the default) when you are measuring a gap: Jan 1 to Jan 8 is 7 days because seven days pass between them. Tick "Include the end date" when you are counting calendar days touched, like vacation days or a pay period: that same span now reads as 8 days because both Jan 1 and Jan 8 are days you were off.

Decimal weeks are easier to compare, average, or multiply. Whole weeks plus remainder days read more naturally. The calculator derives both from the same integer day count. For example, 26 days = 3.7143 weeks = 3 weeks and 5 days after display rounding.

Calendar months range from 28 to 31 days, so a "5 month" pregnancy could span 140 to 153 days depending on which months you cross. Weeks are always 7 days, so dating a pregnancy in weeks gives the clinician a single precise number that maps cleanly onto fetal-development milestones. Standard obstetric dating is 40 weeks from the last menstrual period. Early term begins at 37 weeks, while full term begins at 39 weeks.