# Week calculator from date

Counts the weeks from one date to another: whole weeks and days, the same span as a decimal number of weeks, and in months and days.

- Page: https://www.acalculator.org/days/weeks-calculator
- JSON spec: https://www.acalculator.org/days/weeks-calculator.json
- Version: ffe7c75c96e6

## Default answer

Example with the default inputs (From date September 30, 2026, To date December 23, 2026) on the example date Wednesday, September 30, 2026: From September 30, 2026 to December 23, 2026 is 12 weeks.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| start | From date | The date to count from. Today, unless you change it. |
| end | To date | The date to count to. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| weeks | Weeks | Whole weeks and the days left from the start date to the end date. |
| decimal | In weeks | The days ÷ 7, as a decimal number of weeks. |
| days | Days | Calendar days from the start date to the end date. |
| span | In years, months, and days | The time from the start date to the end date as whole years, then whole months, then days. |

## Method

days = to date − from date; weeks = days ÷ 7 rounded down, with days − 7 × weeks days left

## Assumptions

- Dates are whole calendar days in the Gregorian calendar, with no time of day.
- The from date is not counted and the to date is: from a Monday to the next Monday is 1 week.
- The from date is today unless you change it; the page reads today’s date from your device when it loads.
- A from date after the to date has no answer.

## Worked examples

1. start = 2026-09-30, end = 2026-12-25 gives weeks = {"weeks":12,"days":2}, decimal = 12.285714, days = 86, span = {"years":0,"months":2,"days":25}. Source: Julian Day numbers (Meeus, Astronomical Algorithms, 1991, chapter 7): JD 2461399.5 − JD 2461313.5 = 86 days.
2. start = 2026-01-01, end = 2026-12-31 gives weeks = {"weeks":52,"days":0}, decimal = 52, days = 364. Source: Gregorian calendar (ISO 8601): a common year has 365 days, 52 weeks and 1 day.
3. start = 2024-02-01, end = 2024-03-01 gives weeks = {"weeks":4,"days":1}, decimal = 4.142857, days = 29. Source: Gregorian leap-year rule (ISO 8601).

## FAQ

### How do I count the weeks between two dates?

Count the days from the first date to the second, then divide by 7. The whole number is the weeks and the remainder is the days left. From September 30 to December 25, 2026 is 86 days, and 86 = 12 × 7 + 2, so 12 weeks and 2 days.

### How many weeks are there until a date?

Leave the from date as today and enter the date as the to date. The page reads today’s date from your device when it loads, so the count is right on the day you open it.

### What does the decimal number of weeks mean?

It is the days divided by 7, so 12 weeks and 2 days is 86 ÷ 7 = 12.29 weeks. Use it when a form asks for weeks with a decimal point.

### Is the first day counted?

No. The count is the days from the from date up to the to date, so from a Monday to the next Monday is 7 days, which is 1 week. The same date twice is 0 weeks.

### How many weeks are in a year?

A common year has 365 days, which is 52 weeks and 1 day; a leap year has 366 days, 52 weeks and 2 days. From January 1 to December 31 of a common year is 364 days, exactly 52 weeks.

### Can the to date be before the from date?

No. If the to date is before the from date there is no answer; swap the two dates.

## Sources

- Jean Meeus, Astronomical Algorithms (1991), chapter 7: Julian Day numbers, so the days between two dates are the difference of their Julian Days.
- ISO 8601, Date and time format: the Gregorian calendar, its leap-year rule, and the 7-day week.