Leases, subscriptions, probation periods, warranties and follow-up appointments are measured in months, but a month is not a fixed number of days. This calculator adds or subtracts calendar months the way people and contracts usually mean it: the same day of the month, a few months on. It also deals with the awkward cases, such as adding a month to January 31.
How to use the months from date calculator
- Enter the start date.
- Enter the number of months — 3, 6, 12, 18 or any other whole number.
- Choose after or before the start date.
- Read the date, the weekday, and the exact number of days that period contains.
Months from date formula
Day = the smaller of the start day and the number of days in the new month
Counting months as a running index from year zero avoids year-end arithmetic: dividing by 12 gives the year, and the remainder gives the month. Then the day is clamped to the length of that month, which produces the end-of-month rule.
Worked example: 6 months from October 15, 2026
- October is month 10. Adding 6 gives month 16, which is month 4 of the next year: April 2027.
- The day stays 15; April has 30 days, so no adjustment is needed.
- Result: Thursday, April 15, 2027.
- Days in that period: 182 — more than 6 × 30 because several of the months have 31 days.
The end-of-month rule: adding months to January 31, 2026
When the start day does not exist in the target month, the result is the last day of that month. The table below, computed with the same rule, shows why “one month” after January 31 is not the same as 31 days.
| Months added | Result | Days elapsed |
|---|---|---|
| 1 | Saturday, February 28, 2026 | 28 |
| 2 | Tuesday, March 31, 2026 | 59 |
| 3 | Thursday, April 30, 2026 | 89 |
| 4 | Sunday, May 31, 2026 | 120 |
| 5 | Tuesday, June 30, 2026 | 150 |
| 6 | Friday, July 31, 2026 | 181 |
Months after October 15, 2026
| Months | Date | Days elapsed |
|---|---|---|
| 1 | Sunday, November 15, 2026 | 31 |
| 2 | Tuesday, December 15, 2026 | 61 |
| 3 | Friday, January 15, 2027 | 92 |
| 6 | Thursday, April 15, 2027 | 182 |
| 9 | Thursday, July 15, 2027 | 273 |
| 12 | Friday, October 15, 2027 | 365 |
| 18 | Saturday, April 15, 2028 | 548 |
| 24 | Sunday, October 15, 2028 | 731 |
Months, weeks or days?
- Use months for contracts that say “3 months” or “1 year”, billing cycles and lease terms.
- Use days for “30-day” return policies or notice periods stated in days; 30 days is not one month.
- Use weeks for plans such as “12-week program”, which last 84 days regardless of the calendar.
Check the wording of your agreement: some contracts specify that a month ends on the day before the corresponding date, so a lease that starts on the 15th may end on the 14th. In that case, subtract a day from the result.
For other spans use the Weeks From Date Calculator or Days From Date Calculator calculators; to count the gap between two dates, the Date Calculator and Days Until Calculator calculators are the right tools.
Frequently asked questions
What is 6 months from today?
Move the month forward six places and keep the day of the month. 6 months after October 15, 2026 is Thursday, April 15, 2027.
What happens when the target month is shorter?
The date is moved to the last day of that month. January 31 plus one month is February 28 (or 29 in a leap year), not “February 31”. This is the standard rule used by most calendars, spreadsheets and contracts.
Is a month always 30 days?
No. Months have 28 to 31 days, so the number of days in “6 months” varies from about 181 to 184. If a contract means exactly 30 days, use the days-from calculator instead.
How do I find the date 3 months ago?
Choose “Before the start date” and enter 3. The calculator steps back three calendar months and keeps the day, adjusting at month end where needed.
How do I add a year?
Add 12 months. A 12-month step keeps the same calendar date, except February 29, which becomes February 28 in a common year.