Weeks Calculator
Modes
tools in one
Quick Answer
Use 6 modes to calculate weeks: between dates, add/subtract weeks, count weeks until/ago, or find week numbers.
Includes business weeks, ISO week numbers, and detailed breakdowns.
How Weeks Are Calculated
A week equals exactly 7 days. When counting weeks between two dates, the calculator divides the total day difference by 7 to get complete weeks, with the remainder shown as extra days. For business weeks, only Monday–Friday days are counted, and 5 business days make one business week. ISO week numbers follow the ISO 8601 standard, where week 1 contains the first Thursday of January.
Common Week Calculations
| Period | Weeks | Days |
|---|---|---|
| 1 month | ~4.3 | 28–31 |
| 1 quarter | 13 | 91 |
| 6 months | 26 | 182 |
| 1 year | 52 | 365 |
| Pregnancy | 40 | 280 |
ISO Week Numbers Explained
The ISO 8601 standard defines weeks as starting on Monday and ending on Sunday. Week 1 of any year is the week that contains the first Thursday of January. This means some years have 53 ISO weeks instead of 52 — for example, if January 1st falls on a Thursday (non-leap year) or Wednesday/Thursday (leap year). Most European countries, many Asian countries, and international business standards follow ISO week numbering. The United States commonly uses a Sunday-start week convention instead, which can differ by ±1 week from ISO numbering near year boundaries.
Practical Applications
Weeks are the natural unit for agile sprint planning (typically 1–4 week sprints), pregnancy tracking (40 weeks), academic semesters (15–16 weeks), and notice periods (commonly 2–4 weeks). Mortgage and loan terms are often expressed in months but converting to weeks gives a more granular view of remaining time. Project managers frequently use "weeks until deadline" to gauge urgency — a 4-week countdown has a very different feel than hearing "about a month."