Weeks Between Dates Calculator
Enter two dates to instantly calculate the exact number of weeks between them, including full weeks, remaining days, total days, and decimal weeks. Useful for pregnancy tracking, project planning, semester scheduling, and more.
Common Scenarios
Click a scenario to set the end date relative to the start date (or today).
Frequently Asked Questions
How do I calculate weeks between two dates?
To calculate weeks between two dates, find the total number of days separating them and divide by 7. The whole-number part is your full weeks count; the remainder is the extra days. For example, 45 days = 6 full weeks and 3 remaining days. Our calculator does this instantly for any pair of dates.
How many weeks are in a year?
A standard year has exactly 52 weeks and 1 day (365 days ÷ 7 = 52.143 weeks). A leap year has 52 weeks and 2 days (366 days). This is why the same calendar date falls on a different day of the week each year.
How many weeks is a full-term pregnancy?
A full-term pregnancy lasts 40 weeks (280 days) from the last menstrual period (LMP). Doctors track gestational age in weeks. The first trimester covers weeks 1–13, the second trimester weeks 14–27, and the third trimester weeks 28–40.
How many weeks is a college semester?
A typical college semester is 15–16 weeks long (approximately 105–112 days). Some programs use quarters, which are around 10–11 weeks. Enter your semester start and end dates to get an exact week count.
How many weeks is 3 months?
Three calendar months is approximately 13 weeks (91 days), though it varies slightly depending on which months are involved. For example, January through March (non-leap year) is exactly 90 days = 12 weeks and 6 days.
What is the difference between full weeks and decimal weeks?
Full weeks is the integer part of the week count — the number of complete 7-day periods. Decimal weeks expresses the total as a single decimal number (e.g., 10 days = 1.4286 weeks). Decimal weeks are useful for comparisons and calculations, while full weeks + remaining days is more intuitive for scheduling.
Does the order of start and end dates matter?
No. The calculator always returns a positive result regardless of which date is entered as start or end. It uses the absolute difference between the two dates.
How many weeks are between two dates that span a leap year?
Leap years add one extra day (February 29), so a period spanning a full leap year has 366 days = 52 weeks and 2 days instead of the usual 52 weeks and 1 day. Our calculator automatically accounts for leap years in all calculations.
How to Count Weeks Between Two Dates
To count the number of weeks between two dates, find the total number of days separating them and divide by 7. The whole number part gives you complete weeks; the remainder gives extra days. For example, 45 days equals 6 full weeks and 3 remaining days (6 weeks + 3 days).
Formula
Total Days = |Date2 − Date1| in milliseconds ÷ 86,400,000
Full Weeks = Math.floor(Total Days ÷ 7)
Remaining Days = Total Days mod 7
Decimal Weeks = Total Days ÷ 7
The absolute difference ensures the result is always positive, regardless of which date is entered as start or end. The total days are divided by 86,400,000 (the number of milliseconds in one day) and rounded to handle daylight saving time transitions.
Common Week Counts
| Duration | Weeks | Total Days |
|---|---|---|
| 1 month | ~4.3 weeks | 28–31 |
| Quarter (3 months) | 13 weeks | 91 |
| College semester | 15–16 weeks | 105–112 |
| Half year | 26 weeks | 182–183 |
| Full year | 52 weeks | 365–366 |
| 2 years | 104 weeks | 730–731 |
Pregnancy Weeks
A full-term pregnancy lasts approximately 40 weeks (280 days) from the last menstrual period (LMP). Doctors track pregnancy in weeks because fetal development milestones are tied to gestational age in weeks. Each trimester covers roughly 13 weeks:
| Trimester | Weeks | Days |
|---|---|---|
| First trimester | Weeks 1–13 | Days 1–91 |
| Second trimester | Weeks 14–27 | Days 92–189 |
| Third trimester | Weeks 28–40 | Days 190–280 |
To use this calculator for pregnancy: enter your LMP date as the start date and today's date (or your due date) as the end date. The result shows exactly how many weeks pregnant you are and the remaining days within the current week.
Project Planning with Weeks
Weeks are a natural unit for project planning. Sprints in agile development are typically 1–4 weeks; school semesters run 15–16 weeks; fiscal quarters span 13 weeks. Use this calculator to:
- Determine how many sprints fit between a project start and a release date
- Calculate how many weeks remain until a deadline
- Convert a contract duration (e.g., 90 days) into weeks for scheduling
- Find the end date for a fixed-week engagement (use the scenario buttons)
Examples
How many weeks from January 1, 2026 to March 1, 2026?
January has 31 days and February 2026 has 28 days (not a leap year), giving 59 total days. 59 ÷ 7 = 8 full weeks with 3 remaining days (8 weeks, 3 days).
How many weeks are in a school year?
A typical US school year runs from early September to mid-June, roughly 36 weeks (180 instructional days). From September 2 to June 5 is approximately 276 days = 39 weeks and 3 days.
Related Tools
- Date Calculator — Find days between dates or add/subtract days from a date
- Date Add/Subtract Calculator — Add or subtract weeks, months, and years from any date
- Business Days Calculator — Count working days between two dates, excluding weekends
- Age Calculator — Calculate exact age in years, months, and days