How to use this Month Calculator
This free Month Calculator supports three related date tasks without making you switch pages. Use Months Between Dates to count completed months and remaining days. Use Add / Subtract to find a date a specified number of months before or after another date. Use Month Info to check a month’s number of days, weekdays and leap-year status.
- Select the calculation mode in the tool above.
- Enter your dates or month and year.
- Read the instant result. The calendar method is shown beside the result.
- Use Copy Result to save the calculation, or Reset to start over.
How to calculate months between two dates
Calendar months are not all the same length. This tool counts each completed calendar-month anniversary from the earlier date to the later date. A monthly anniversary lands on the same day number where possible; in a shorter month it lands on the last valid day. Any elapsed days after the last completed anniversary appear as extra days.
| Start date | End date | Result |
|---|---|---|
| Jan 1, 2026 | Apr 1, 2026 | 3 months, 0 days |
| Jan 15, 2026 | Mar 20, 2026 | 2 months, 5 days |
| Jan 31, 2026 | Feb 28, 2026 | 1 month, 0 days |
| Jan 31, 2024 | Feb 29, 2024 | 1 month, 0 days |
| Dec 20, 2025 | Jan 1, 2026 | 0 months, 12 days |
Formula (conceptually): completed months = the largest nonnegative whole number m for which start date + m calendar months is on or before the end date. Extra days = end date − that last monthly anniversary.
Add or subtract calendar months
Moving forward or backward by a whole number of months preserves the day of the month whenever possible. If the destination month does not have that day, the date moves to the destination month’s final day. This is commonly called month-end clamping.
| Operation | Result |
|---|---|
| Jan 31, 2026 + 1 month | Feb 28, 2026 |
| Jan 31, 2024 + 1 month | Feb 29, 2024 |
| Mar 31, 2026 − 1 month | Feb 28, 2026 |
| Nov 12, 2026 + 6 months | May 12, 2027 |
Some payroll, finance, and legal systems use different end-of-month conventions. If a contract or statute defines its own method, follow those rules instead of assuming calendar-month clamping applies.
How many days are in each month?
Use the Month Info tab for a selected year. In the Gregorian calendar, February’s length depends on leap-year rules, while other month lengths are fixed.
| Month | Number of days |
|---|---|
| January | 31 |
| February | 28 or 29 |
| March | 31 |
| April | 30 |
| May | 31 |
| June | 30 |
| July | 31 |
| August | 31 |
| September | 30 |
| October | 31 |
| November | 30 |
| December | 31 |
Month Calculator versus Age in Months Calculator
This page is for general month calculations: any two dates, calendar-month addition or subtraction, and month details. If you want the number of completed months since someone’s date of birth, use the dedicated Age in Months Calculator. For inclusive day counting and detailed day/week intervals, use our Date Difference Calculator.
Frequently asked questions
How do I calculate the number of months between two dates?
Choose a starting date and ending date. The tool counts completed calendar months using the start date as the anniversary anchor, then reports the extra elapsed days. It also provides the exact total calendar-day difference.
What is the difference between complete months and total days?
A month may contain 28, 29, 30 or 31 days. Completed calendar months count matching monthly anniversaries; total days count each elapsed calendar date, so you should not convert between them using a fixed 30-day month.
Does January 31 plus one month become February 28?
Yes, in a non-leap year this calculator clamps to February 28 because February 31 does not exist. In a leap year it becomes February 29.
How many months are there from January 31 to February 28, 2026?
Under this page’s month-end anniversary convention, January 31 to February 28, 2026 is 1 completed calendar month and 0 extra days.
Is there a fixed number of days in a month?
No. February has 28 days (29 in a leap year), April, June, September and November have 30, and the other months have 31 days.
How does the calculator handle dates in reverse order?
It calculates the positive elapsed interval between the earlier and later date and displays a note that the entered dates were reversed. Use the Swap Dates control to reverse the inputs.
Are the start date and end date both included?
The elapsed-day count excludes the start date and counts how many midnight-to-midnight calendar dates separate the inputs. For inclusive-day counting, use the Date Difference Calculator.
How do I subtract months from a date?
Open the Add / Subtract tab, select a starting date, choose Subtract, and enter a whole number of months. The result moves backward by that number of calendar months and clamps the day if necessary.
Why might adding and then subtracting a month not return the original date?
Month-end clamping can lose the original day number. For example, January 31 + 1 month becomes February 28 in 2026; subtracting 1 month from February 28 then becomes January 28.
Can I find how many days February has?
Yes. Open Month Info, select February and the year. The tool checks Gregorian leap-year rules and shows 28 or 29 days, first/last weekdays and weekday counts.
Does the result depend on my time zone?
The calculator compares calendar dates, not clock timestamps. Elapsed calendar days are computed from UTC-midnight representations to avoid daylight-saving errors. Today is populated from your device’s local calendar date.
Is this the same as an Age in Months Calculator?
Not quite. This tool compares any two dates or adds and subtracts calendar months. The Age in Months Calculator specializes in the months since a birth date and related age milestones.