When to use this calculator
Find the number of days in a Gregorian month, including leap-year February. Month numbers run from 1 for January to 12 for December.
Explore the calendar dates & age calculators for other questions in this topic. For a related calculation, use the ISO Week Number Calculator: Find ISO week-year and week number for a chosen date.
PUTTING IT INTO PRACTICE
Days in Month: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Year (integer) | 2,028 |
| Month number (integer) | 2 |
| Result | 29 days |
- Check the input labels and enter the example values above.
- Apply the relationship: Use the Gregorian month length and leap-year rule..
- The result is 29 days, rounded for display.
How to interpret your result
Month numbers run from 1 for January to 12 for December.
Choose whether an interval includes the start or end boundary. Month and year additions use explicitly stated clamping rules when a destination day does not exist. Date-only arithmetic is kept independent of local daylight-saving hour shifts.
Frequently asked questions
Does adding one month always add the same number of days?
No. Calendar months vary in length. A day-count addition and a calendar-month addition solve different questions.
When is the days in month calculator useful?
Find the number of days in a Gregorian month, including leap-year February. Month numbers run from 1 for January to 12 for December.
How do I use the days in month calculator?
Enter year (integer), month number (integer). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Use the Gregorian month length and leap-year rule..
What should I check before using the result?
Month numbers run from 1 for January to 12 for December.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see MDN: date values and calendar handling ↗. This is a topic reference, not an external review or endorsement of this tool.
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