How the day count works
The calculator subtracts your start date from your end date to find the number of whole days between them. By default it counts the days from your start date up to your end date, which excludes the end day. Turning on Include the end day adds one day, so both the first and last day are counted.
The same total is also shown as a calendar breakdown - years, months, and days - and as weeks and days. Because months vary in length, the calendar breakdown counts whole months from your start date and then the leftover days, so it lines up with how people actually read dates on a calendar.
Common ways to use it
- How many days since your last period started
- How many days until your due date or next appointment
- How long it has been since any milestone or event
- Counting nights for a trip (leave the end day out)
Frequently asked questions
How do I count the number of days between two dates?
Enter a start date and an end date, and the calculator subtracts one from the other to give the whole number of days between them. By default the start day is counted but the end day is not; turn on 'Include the end day' to count both.
Should I include the end day?
It depends on what you are counting. To count nights between two dates (like a hotel stay), leave the end day out. To count the total number of calendar days an event covers, including both the first and last day, include the end day - it adds one to the total.
Why does the years-and-months breakdown differ from just dividing days?
Months and years are not all the same length, so the calendar breakdown counts whole months from your start date (clamping to each month's length) and then the leftover days. That is why '1 month' can be 28, 30, or 31 days depending on where it falls.
Does it matter which date I put first?
No. The calculator works whether your earlier date is in the 'from' or 'to' field - it always shows the duration between them and notes when the end date is before the start date.
Can I use this for my cycle or pregnancy?
Yes. It is handy for counting the days since your last period, the days until your due date, or how long it has been since any event. For cycle-specific predictions, the period, ovulation, and due date calculators do the cycle math for you.