Weeks Between Dates

How the weeks-between algorithm works: The calculator subtracts the start date from the end date in milliseconds, divides by 86,400,000 to get total days, then computes whole weeks as days divided by 7 floored, remaining days as days modulo 7, and total weeks as days divided by 7 rounded to two decimals. The dates are handled in either order, using the absolute difference. The result shows both the compact format like 4 weeks 3 days and the decimal like 4.43 weeks total.

Whole weeks versus decimal weeks: The whole-weeks-plus-rem format like 4 weeks 3 days is intuitive for scheduling. The decimal format like 4.43 weeks is useful for financial calculations, prorated billing, and project tracking where partial weeks matter. Austin agencies use 4.43-week reports for $50,000 campaign pacing. Chicago firms use 8.71-week totals for $10,000 discovery budgets. Miami planners use 26.00-week timelines for $30,000 weddings. Denver contractors use 16.00-week phases for $200,000 builds.

Pregnancy and healthcare tracking: The weeks-and-days format matches how pregnancy is commonly quoted. A 40-week pregnancy spans approximately 280 days. A 12-week first-trimester window is 84 days. Seattle healthcare providers use this for prenatal milestone tracking. Miami clinics use it for 26-week prenatal-care windows. Austin hospitals use it for 40-week due-date calculations. Denver midwives use it for 36-week viability markers. New York OB-GYNs use it for 10-week postpartum follow-up windows.

Project and contract timeline scenarios: Austin agencies track 12-week $50,000 campaign sprints from 01/06 to 03/30. Chicago law firms compute 8-week $10,000 discovery periods from 03/15 to 05/10. Miami event planners track 26-week $30,000 engagement timelines from 06/01 to 12/01. Denver construction crews count 16-week $200,000 build phases from 09/01 to 12/21. Seattle nonprofits measure 52-week $80,000 annual programs from 01/01 to 12/31. New York publishers track 10-week $15,000 editorial cycles from 09/01 to 11/10.

Edge cases and date handling: Same-day spans return 0 weeks 0 days. Reversed dates automatically swap. Spans crossing February compute correctly whether the year is leap or common. The tool uses midnight-to-midnight counting. Very large spans like multi-year contracts show accurate week and day counts. All math runs locally in your browser with no uploads, keeping sensitive scheduling data private.