Weeks Between Two Dates

How weeks are calculated

The number of complete weeks between two dates is the total number of days divided by 7, rounded down. The remaining days (0 to 6) represent the partial week. For example, 45 days = 6 weeks and 3 days. The Flowfiles date calculator shows this breakdown alongside the total day count.

A week is always 7 days, regardless of which days of the week it spans. A period from Wednesday to the following Tuesday is exactly one week (7 days), even though it does not align with a Monday–Sunday calendar week. This is important when a cycle or commitment is expressed as "one week from today" rather than "the calendar week of".

Agile sprints and project planning

Agile development uses fixed-length iterations called sprints, typically one or two weeks. A two-week sprint starting Monday and ending the following Friday spans 14 calendar days (2 weeks exactly) and contains 10 business days. The sprint retrospective, review and planning ceremonies happen at the boundary between sprints.

When planning a quarter (13 weeks) or a project of several months, expressing scope in sprint counts rather than calendar months avoids ambiguity. "This feature will take 3 sprints" is clearer than "about 6 weeks" when sprints are two weeks, because "6 weeks" might be interpreted as 42 days but the actual available working time is 30 business days.

• 1-week sprint — 5 business days, useful for high-cadence teams
• 2-week sprint — 10 business days, the most common cadence
• 4-week sprint (monthly) — 20 business days, common in hardware or regulated environments

Pregnancy and gestational weeks

Pregnancy duration is measured in gestational weeks, counted from the first day of the last menstrual period (LMP). Week 1 begins on the LMP date. A full-term pregnancy is 40 weeks (280 days) from LMP. Trimester divisions are weeks 1–13 (first), 14–26 (second) and 27–40 (third).

To find your current gestational week, enter the first day of your LMP as the start date and today's date as the end date in the date calculator. The result in weeks and days corresponds to your gestational age. The estimated due date (EDD) is 280 days from the LMP, which you can calculate using the Add / Subtract tab by adding 280 days to your LMP.

Note that gestational age calculated from LMP differs from actual embryonic age (which starts at fertilisation, roughly 2 weeks after LMP). Clinical practice uses gestational age consistently.

Subscription and billing cycles

Some billing systems charge on a weekly or bi-weekly basis rather than monthly. A 13-week quarterly subscription renewed on a weekday contains exactly 13 billing cycles of 7 days each. If the subscription started on April 1, the 13th payment date is June 30 — not July 1.

Weekly billing is also common in payroll (bi-weekly pay every 14 days) and in short-term rentals, storage units and some streaming services. Knowing how many weeks fall in a given period helps reconcile billing statements and project cash flow accurately.

Frequently asked questions