Weeks Calculator

What Is a Weeks Calculator?

A weeks calculator converts between weeks and other time units, calculates the number of weeks between two dates, or finds a date a specified number of weeks in the future or past. How many weeks until summer vacation? How many weeks pregnant are you? What date is 12 weeks from today? Enter your dates or values in the calculator above for instant conversion between weeks, days, months, hours, and minutes with precise results for any time span.

Weeks to Days and Other Conversions

1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds. 2 weeks = 14 days (a fortnight). 4 weeks = 28 days (not exactly 1 month). 13 weeks = 91 days (approximately 1 quarter). 26 weeks = 182 days (approximately 6 months). 52 weeks = 364 days (1 day short of a year). A common source of confusion: 4 weeks is not equal to 1 month because months have 28-31 days. Similarly, 52 weeks is not exactly 1 year because 52 times 7 = 364, one day short. This one-day discrepancy is why the same date falls on a different day of the week each year in a regular year and shifts by two days in a leap year.

Weeks in Pregnancy

Pregnancy is measured in weeks from the first day of the last menstrual period (LMP), totaling approximately 40 weeks (280 days). First trimester: weeks 1-12. Second trimester: weeks 13-26. Third trimester: weeks 27-40. Each prenatal visit tracks progress by week number, and developmental milestones are referenced by gestational week. Enter your LMP date to calculate your current week of pregnancy, estimated due date, and trimester. Premature birth is defined as before 37 weeks. Full term is 39-40 weeks. Post-term is beyond 42 weeks. These weekly benchmarks guide medical decisions throughout the entire pregnancy journey.

Weeks in Business and Project Management

Project timelines are frequently planned in weeks. A 12-week product development sprint. A 6-week marketing campaign. An 8-week training program. A 52-week rolling forecast. Agile software development uses 1-2 week sprints as the fundamental planning unit. Academic semesters are typically 15-16 weeks. Corporate quarters are 13 weeks. Fiscal years are 52 or 53 weeks (the 53-week year occurs roughly every 5-6 years in retail 4-4-5 calendar systems). Planning in weeks provides more granularity than months while remaining practical for scheduling meetings, milestones, and deliverables across team calendars.

How Many Weeks Between Two Dates?

Divide the number of days between two dates by 7. From January 1 to April 1 (90 days in a non-leap year): 90 / 7 = 12 weeks and 6 days. The calculator shows both the exact number of complete weeks and the remaining days. For business planning, partial weeks are often rounded up (a task spanning 12 weeks and 6 days is planned as 13 weeks). For pregnancy tracking, partial weeks are typically expressed as "12 weeks and 6 days" or "12+6" in standard medical notation used by obstetricians and midwives worldwide.

Weeks Between Two Dates: Worked Examples

The examples below show how the calculator counts. Every result is the day difference divided by 7, with the remainder reported as extra days.

The last row explains a calendar quirk: January 1 to December 31 covers 364 days, which is 52 clean weeks, yet the year itself has 365 days because the count between two dates excludes one endpoint. Whether you include both endpoints changes the answer by one day, and by one day only. The calculator above counts from the start date up to, but not including, the end date, which matches how project schedules and gestational age are counted.

How Many Weeks in a Year, a Month, and a Quarter?

A regular year has 365 days, which is 52 weeks and 1 day (52.14 weeks). A leap year has 52 weeks and 2 days. The average month is 30.44 days, or 4.35 weeks. February is the only month that can equal exactly 4 weeks, and only outside leap years. A quarter is 13 weeks in the 4-4-5 retail calendar and roughly 13.04 weeks on the standard calendar. Half a year comes to about 26.07 weeks. These figures explain why a weekly habit done every week still produces 52 sessions in some years and 53 in others: the leftover day or two eventually stacks into a full extra week.

Adding Weeks to a Date

To add weeks, multiply by 7 and add the days. Adding 12 weeks to March 2, 2026 means adding 84 days, which lands on May 25, 2026. One property makes whole-week addition useful for scheduling: the result always falls on the same weekday as the start. March 2, 2026 is a Monday, and so is May 25, 2026. A 6-week notice period given on a Friday ends on a Friday. An 8-week course that starts on a Tuesday holds its final session on a Tuesday. The calculator handles the reverse direction too: subtract weeks from a deadline to find when work has to start.

Week Numbers and the ISO Calendar

Many planners, payroll systems, and European documents refer to dates by week number instead of by month and day. The ISO 8601 standard defines week 1 as the week containing the first Thursday of the year, with every week starting on Monday. Under this rule a year has either 52 or 53 numbered weeks, and the first days of January can belong to week 52 or 53 of the previous year. US calendars often start weeks on Sunday instead, which is why the week number printed in an American planner can differ from the one in a European shipping schedule for the same date. When someone quotes a delivery in "week 37," confirm which convention they use before booking anything around it.

Weekly Patterns and Schedules

Many recurring activities follow weekly cycles. Payroll is processed weekly or biweekly (every 2 weeks). Biweekly pay results in 26 paychecks per year, not 24 (which would be semi-monthly). Mortgage payments can be set to biweekly, resulting in 26 half-payments per year, equivalent to 13 full monthly payments instead of 12, which pays off the loan faster and saves substantial interest. Weekly grocery spending, exercise schedules, medication dosing, and appointment scheduling all benefit from thinking in weeks rather than months because weeks are perfectly consistent at 7 days while months vary from 28 to 31.

Converting Weeks to Months

Because months have different lengths, the weeks-to-months conversion is approximate. 4 weeks = 28 days (slightly less than any month). 4.33 weeks = average month (30.44 days / 7). Common approximations: 6 weeks = about 1.5 months. 8 weeks = about 2 months. 12 weeks = about 3 months. 16 weeks = about 4 months. 20 weeks = about 5 months. For precise conversions, use exact dates rather than approximate month equivalents. The calculator provides both week counts and equivalent month-and-day breakdowns for any date range you need to analyze or communicate to others. This dual display eliminates the ambiguity that arises when different people interpret week-to-month conversions differently.

Frequently asked questions