How the days between dates calculator is calculated
weeks = days ÷ 7, with the days left over
months = whole months counted from the start date's day of the month, then the days left over
Worked example: 1 October to 10 November 2026
Enter 1 Oct 2026 as the start date and 10 Nov 2026 as the end date to reproduce this table. The calculator loads with a start date 40 days ago and today as the end date, so it opens on a 40 day answer too.
| Line | Amount |
|---|---|
| Calendar days, end day not counted | 40 |
| In weeks | 5 weeks, 5 days |
| In months | 1 month, 9 days |
| Calendar days, end day counted | 41 |
| Second example: 15 Jan to 15 Mar 2026 | 59 days, 8 weeks, 3 days, 2 months |
Every default in the calculator is an example so you can see a result straight away. None is a market average. Replace each with your own costs and rates.
Count the days between, or count both ends?
Counting from 1 October to 10 November gives 40 days: the difference between the two dates. If both the first and the last day count, as they do for a hotel stay or a rental period, the same range is 41 days. Payment terms count the first way. Net 30 on an invoice dated 1 October falls on 31 October, 30 days later, not on 30 October.
Months are not a fixed length
A month here means the same day of the next month. 1 October to 1 November is one month even though it is 31 days, and 1 November to 1 December is one month at 30 days. If the start day does not exist in a later month, such as the 31st, the last day of that month is used. For a count that skips weekends, use the business days calculator.
Leap years
The count uses the real calendar, so 29 February is counted in a leap year. From 29 Feb 2024 to 28 Feb 2025 is 365 days and 11 months, 30 days, because 28 Feb 2025 falls one day short of a full year.
Put the dates on an invoice
Once you know the gap, set the dates on the document. Open the invoice generator and pick the issue date and due date, or use the invoice due date calculator to work the due date out from your payment terms. For an invoice that has already gone late, the days past due calculator shows how many days overdue it is. Freelancers can find the invoice designs on the freelancer invoice page.
Related calculators
- Business days calculatorAdd, subtract or count working days
- Invoice due date calculatorFind the due date from your payment terms
- Days past due calculatorHow late an invoice is and what it costs
Questions people ask
How many days are there between two dates?
Subtract the earlier date from the later one. From 1 October 2026 to 10 November 2026 that is 40 days. The calculator does the subtraction on calendar dates, so months of different lengths and leap years are handled.
How do I count days including the end date?
Add one to the difference. The same range, 1 October to 10 November 2026, is 41 days when both the first and the last day count. Choose Yes under Count the end day too.
How do I find how many days ago an invoice was dated?
Enter the invoice date as the start date and leave the end date empty. Empty means today, so the answer is the invoice age in days. For overdue invoices the days past due calculator also applies your payment terms.
How many weeks and months is that?
Weeks are the days divided by 7. Months are whole months counted from the start date's day of the month, with the leftover days shown. 59 days from 15 Jan to 15 Mar 2026 is 8 weeks and 3 days, or exactly 2 months.
Does the calculator skip weekends?
No. It counts every calendar day. To count only Monday to Friday, use the business days calculator, which also shows the weekend days it skipped.