What this calculator does
Most months have a fixed length that never changes, but it is easy to blank on the exact number when planning a billing cycle, a due date or a roster. This calculator answers how many days in Jan, June, November or any other month, and handles the one month that genuinely varies: February.
February has 28 days in a normal year and 29 in a leap year. A leap year is any year divisible by 4, except century years (divisible by 100) unless they are also divisible by 400, which is why 2000 was a leap year but 1900 was not. Every other month keeps the same length every single year.
The formula
Every month from March through January has a fixed number of days that never changes. February is the exception: it has 28 days, or 29 in a leap year. A year is a leap year if it divides evenly by 4, unless it also divides evenly by 100, in which case it is only a leap year if it divides evenly by 400 too.
| Term | Meaning |
|---|---|
| Leap year | A year with an extra day in February (29 instead of 28), added to keep the calendar aligned with the solar year. |
| Common year | Any year that is not a leap year, with 365 days total and 28 in February. |
The inputs explained
| Field | What to enter |
|---|---|
| Month | Pick the month you want the day count for. |
| Year (only matters for February) | Only affects the result if you selected February; ignored for every other month. |
When to use it
Setting up a monthly billing cycle
Knowing exactly how many days fall in a given month avoids off-by-one errors when pro-rating a subscription or invoice that starts or ends partway through it.
Checking if a specific year is a leap year
Selecting February for any year instantly shows whether that year has the extra day, without having to work through the divisibility rule by hand.
Planning around February in advance
Anyone rostering shifts, booking travel or setting a recurring reminder for the end of February needs to know in advance whether it runs to the 28th or the 29th.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How many days does each month have?
Every month in a common year, for quick reference.
| Month | Days in the month |
|---|---|
| January | 31 days |
| February | 28 days |
| March | 31 days |
| April | 30 days |
| May | 31 days |
| June | 30 days |
| July | 31 days |
| August | 31 days |
| September | 30 days |
| October | 31 days |
| November | 30 days |
| December | 31 days |
Does February change length across nearby years?
February specifically, checked against a spread of years including two century years.
| Year | Days in February | Is it a leap year? |
|---|---|---|
| 2023 | 28 days | No |
| 2024 | 29 days | Yes |
| 2025 | 28 days | No |
| 2028 | 29 days | Yes |
| 1900 | 28 days | No |
| 2000 | 29 days | Yes |
Questions
How many days in Jan?
January always has 31 days, regardless of the year. It is one of the seven months (along with March, May, July, August, October and December) fixed at 31 days.
Why does February change length?
The Earth actually takes about 365.24 days to orbit the sun, not an even 365. Adding a leap day to February roughly every four years keeps the calendar from slowly drifting out of sync with the seasons.
Is every year divisible by 4 a leap year?
Almost, but not quite. Century years (like 1900 or 2100) are the exception: they are only leap years if they also divide evenly by 400. That is why 2000 was a leap year but 1900 and 2100 are not.
How many days does a full year have?
A common year has 365 days and a leap year has 366, the extra day coming entirely from February having 29 days instead of 28.
To count the number of days between two specific dates rather than within one month, see the days calculator. For working out a date a set number of days or months from today, see the date months ago/from now calculator.