Week Calculator
Find the exact number of weeks between any two dates, or count weeks from today to any event — instantly and for free.
Last updated: March 2026
How to Use the Week Calculator
- Select a mode — Use "Weeks Between Dates" to measure the gap between any two calendar dates, or "Weeks From Today" to count weeks until (or since) a specific event.
- Enter your dates — Click or type dates using the date picker. "Weeks From Today" automatically uses today as the start date.
- Read results instantly — You'll see complete weeks, leftover days, total days, decimal weeks, and an approximate month count.
- Share your result — Click Share to copy a pre-filled link, or Clear to start fresh.
How the Week Calculator Works
The calculator computes the absolute day difference between two dates, then applies simple integer division to extract weeks and remaining days.
The Core Formula
Given a start date S and end date E:
- Total days = |E − S| (absolute value, so order doesn't matter)
- Complete weeks = Math.floor(total days / 7)
- Remaining days = total days mod 7
- Decimal weeks = total days / 7
Dates are parsed in UTC to avoid daylight saving time (DST) shifts distorting the count — a common source of off-by-one errors in date calculators.
Worked Examples
- Project timeline: Jan 15 to Apr 20 → 95 days → 13 complete weeks, 4 remaining days
- Weeks pregnant: LMP Mar 1 to today (Jun 15) → 106 days → 15 weeks, 1 day
- Weeks until vacation: Today (Mar 4) to Jul 4 → 122 days → 17 weeks, 3 days
- Contract duration: Feb 1 to Aug 31 → 211 days → 30 weeks, 1 day
Why Count in Weeks?
Weeks occupy a unique middle ground in time measurement — longer than days but more precise than months. For planning and tracking purposes, they are often the most natural unit.
Pregnancy is tracked week-by-week for good reason: fetal development milestones align with 7-day increments, and gestational age in weeks tells doctors far more than months or trimesters alone. Knowing you are "28 weeks and 3 days" is clinically meaningful in a way that "about 7 months" is not.
Project management uses weekly sprints in Agile and Scrum frameworks. Counting the weeks available for a project gives teams a concrete sprint budget to allocate work against. A 10-week project has roughly 10 sprint cycles — a far more actionable number than "about 2.5 months."
Fitness programs are structured in week-long training blocks. A 12-week marathon training plan, a 6-week strength program, or a 4-week cut phase all use weeks because the 7-day rest-and-recovery cycle aligns naturally with the human body's adaptation rhythm.
Academic calendars publish semester lengths in weeks (typically 15–17 weeks per semester), making it easy to plan study schedules and assignment deadlines on a week-by-week basis.
Weeks in Common Time Periods
Understanding how weeks map to other time units helps put calculations in context:
- 1 month (28 days) = 4 weeks exactly
- 1 month (30 days) = 4 weeks 2 days
- 1 month (31 days) = 4 weeks 3 days
- 1 quarter (91 days) = 13 weeks exactly
- 1 year (365 days) = 52 weeks 1 day
- 1 leap year (366 days) = 52 weeks 2 days
- Pregnancy (280 days) = 40 weeks exactly
- School semester (105 days) = 15 weeks exactly
How Many Weeks If...
How many weeks until New Year?
From March 4, 2026, there are approximately 43 weeks until January 1, 2027. The exact count is 303 days, which equals 43 complete weeks and 2 remaining days. Use "Weeks From Today" mode and enter January 1, 2027 for an exact real-time count.
How many weeks in 6 months?
Six months is approximately 26 weeks. The exact value depends on which 6 months you count (February is shorter), but 6 × 30.44 average days ÷ 7 ≈ 26.1 weeks. For any specific 6-month period, use the calculator with exact dates.
How many weeks in 3 months?
Three months is approximately 13 weeks. One calendar quarter (91 days) divides evenly into exactly 13 weeks. This is why quarterly financial reporting periods align so neatly with weekly business rhythms.
How many weeks is 100 days?
100 days is 14 weeks and 2 days (14 × 7 = 98, plus 2 remaining). As a decimal, 100 ÷ 7 = 14.286 weeks. Many political milestones ("first 100 days") and fitness challenges use 100-day windows.
How many weeks until summer?
From March 4, 2026, there are approximately 15 weeks until the summer solstice on June 21, 2026 — specifically 109 days = 15 weeks 4 days. Memorial Day (May 25) is about 12 weeks away.
How many weeks is a trimester?
Each pregnancy trimester is approximately 13 weeks. The first trimester is weeks 1–13, the second is weeks 14–26, and the third is weeks 27–40. This maps closely to 3-month calendar quarters.
How many weeks between January 1 and December 31?
There are 52 complete weeks and 0 remaining days between January 1 and December 31 (364 days ÷ 7 = 52 exactly). The full year January 1 to December 31 inclusive spans 365 days = 52 weeks 1 day.
How many weeks is a 90-day notice period?
A 90-day notice period is 12 weeks and 6 days. 90 ÷ 7 = 12.857 weeks. For practical planning, this is close to 13 weeks or one calendar quarter.
People Also Search For
How to calculate weeks pregnant from last period
Enter the first day of your last menstrual period (LMP) as the start date and today as the end date in "Weeks Between Dates" mode. The complete weeks result is your gestational age in weeks. Most OB/GYNs use this same LMP-based calculation. Note that ultrasound dating may differ by a few days.
How many weeks until my due date?
Enter today as your start date and your due date as the end date. The result gives you the weeks remaining in your pregnancy. A standard full-term pregnancy is 40 weeks from LMP, so if you're at week 28, you have approximately 12 weeks to go.
How to calculate weeks for a project deadline
Enter today's date as the start and your project deadline as the end in "Weeks Between Dates" mode. The complete weeks count tells you how many full sprint cycles are available. Divide remaining work by sprint capacity to see if your timeline is achievable.
How many weeks between two specific dates in Excel?
In Excel, use =INT((B1-A1)/7) for complete weeks and =MOD(B1-A1,7) for remaining days, where A1 is the start date and B1 is the end date formatted as dates. For decimal weeks: =(B1-A1)/7.
How many weeks is a school year?
A US school year is typically 36 weeks of instruction. The academic calendar runs approximately September through June, but instructional weeks exclude holiday breaks and professional development days. Individual districts may vary between 34 and 38 instructional weeks.
Frequently Asked Questions
How do I calculate the number of weeks between two dates?
Subtract the earlier date from the later date to get total days, then divide by 7. The whole number is complete weeks; the remainder is leftover days. The calculator does this automatically when you enter both dates.
How many weeks are in a year?
A standard year has 52 complete weeks plus 1 extra day (365 ÷ 7 = 52 remainder 1). A leap year has 52 weeks and 2 extra days. Every calendar year spans parts of 53 different ISO calendar weeks.
How many weeks are in a month?
Months vary: February (28 days) = exactly 4 weeks; 30-day months = 4 weeks 2 days; 31-day months = 4 weeks 3 days. The average month is about 4.35 weeks (365 ÷ 12 ÷ 7).
Can this calculator track pregnancy weeks?
Yes. Enter the first day of your last menstrual period (LMP) as the start date and today as the end date. The complete weeks result is your gestational age. A full-term pregnancy is 40 weeks from LMP.
What is a decimal week?
A decimal week expresses the fractional week as a decimal rather than "X weeks Y days." For example, 9 weeks 3 days = 9.43 weeks (66 total days ÷ 7). This format is useful for spreadsheet calculations and financial accruals.
Does the calculator account for leap years?
Yes. The calculator uses JavaScript Date objects which correctly account for leap years (366 days) and all calendar irregularities. Any date range spanning February 29 will be counted accurately.
What is the difference between calendar weeks and work weeks?
A calendar week is any 7-day period. A work week covers Monday through Friday (5 days). For business timelines, use the Working Days Calculator to exclude weekends. This calculator counts full 7-day calendar weeks.
Can I calculate weeks for dates in the past?
Yes. Enter any past dates as start and end. The result is always a positive number — the calculator uses the absolute difference so order doesn't matter. You can calculate how many weeks ago any event occurred.
Is my data private?
All calculations run entirely in your browser. No dates are sent to any server, and nothing is stored or logged. Your inputs are completely private.
How many weeks is 1,000 days?
1,000 days is 142 complete weeks and 6 remaining days (142 × 7 = 994, plus 6). As a decimal, 1,000 ÷ 7 ≈ 142.857 weeks. This is about 2 years and 9 months.