Example 1
- Mode: days between
- 2026-01-01
- 2026-01-31
30
How many days are 1 January 2026 to 31 January? 30 days, not 31.
Date Calculator
The calculator counts full civil days between two dates, or adds a number of days to a date. 1 January 2026 to 31 January is 30 days. 1 January plus 90 days is 1 April.
Days only, without adding, are on difference between dates. Adding only: add days to a date. Clock times: time duration.
Result
Choose a mode and enter the dates. The result will appear here.
How it works
In days-between mode the calculator subtracts the start midnight from the end midnight in UTC. 1 January 2026 to 31 January is 30 days, not 31. That is a 30-day span, not the 31 days of January.
In add mode full midnights are added to the start date. 1 January 2026 plus 90 days is 1 April 2026. 28 February 2024 plus 1 day is 29 February, because 2024 is a leap year.
The day count must be a whole number. A minus subtracts: 1 April 2026 plus −90 is 1 January again.
When the end date is earlier than the start, the calculator asks you to swap the fields. It does not flip the sign on its own.
Clock times, a time zone and daylight saving are not used. Working days belong on a separate page.
This is not a timesheet. A span with hours belongs on the time duration page. Related pages cover a days-only span or adding days to a date.
Formula
days = (end − start) / 86,400 s; date = start + N × 86,400 s
Both operations use UTC midnight. 1 January → 31 January is 30, not 31.
How to use
- Choose days-between mode. Enter 2026-01-01 and 2026-01-31. The result is 30.
- Switch to add. Leave 2026-01-01 as the start date and enter 90. The result is 2026-04-01.
- Enter 2024-02-28 and 1. The result is 2024-02-29.
- Minus 90 from 2026-04-01 returns 2026-01-01.
30 days from 1 to 31 January
From midnight on 1 January to midnight on 31 January, 30 days pass. The 31st does not close a full month.
- 30
- 1 January → 31 January 2026. That is not 31 days.
- 90
- 1 January 2026 plus 90 midnights is 1 April.
- 29 II
- 2024-02-28 plus 1. In a common year that would be 1 March.
Examples
Example 2
- Mode: add days
- 2026-01-01
- 90 days
2026-04-01
What date is 90 days after 1 January 2026? 1 April 2026.
Example 3
- Mode: add days
- 2024-02-28
- 1 day
2024-02-29
What date is the day after 28 February 2024? 29 February, because it is a leap year.
Related calculators
Frequently asked questions
How many days are 1 January to 31 January 2026?
30 days, not 31. Full midnights are counted.
What date is 90 days after 1 January 2026?
1 April 2026.
What is 28 February 2024 plus 1 day?
29 February 2024. In a common year it would be 1 March.
Do clock times enter?
No. Use the time duration page for that.
Are working days removed?
No. Working days belong on a separate page.
Can I subtract days?
Yes. In add mode enter a negative number.
What if the end is before the start?
The calculator asks you to swap the fields.
How is this different from date difference?
This page has two modes: span and add. The date difference page covers only the span between dates.
Sources
A civil day is 86,400 seconds from UTC midnight, without a time zone.
Page updated in 2026.