Month Calculator
Month Calculator works out Days between and Days counting both dates from Start date, End date and Count the end date as a whole day. The default figures on this page give whole months of 32 months; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
6 steps
- Start 2024-01-01 (Monday), end 2026-09-14 (Monday).
- Elapsed days = day number of 2026-09-14 minus day number of 2024-01-01 = 987.
- Calendar walk: 2024-01-01 + 2 year(s) + 8 month(s) + 13 day(s) = 2026-09-14.
- 987 days = 141 week(s) and 0 day(s).
- Decimal years = 987 / 365.2425 (mean Gregorian year) = 2.7023.
- Business days 2024-01-01 to 2026-09-14 inclusive = 706 weekday(s) - 29 holiday(s) = 677.
Holidays in the spantable
Its 10 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
6 sources
What the Month Calculator calculates
Days, weeks, months and years between two calendar dates, with the calendar breakdown, the business-day count and the weekday of each date; it also measures between two date-and-time instants, counts the time elapsed since a date up to today, reports length of service, and lists the sobriety milestones passed.
How to use this Month Calculator
Enter Start date, End date, Count the end date as a whole day and Holidays to exclude from business days. Days between updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Days between, Days counting both dates and Whole years.
The method follows ISO 8601-1:2019, Date and time - Representations for information interchange, Howard Hinnant, chrono-Compatible Low-Level Date Algorithms (days_from_civil), Microsoft Excel NETWORKDAYS function specification, 5 U.S.C. 6103 - Federal legal public holidays and Alcoholics Anonymous sobriety chip practice (24 hours; 30, 60 and 90 days; 6 and 9 months; 1 year, 18 months and each year after).
What you can compare
Change one input at a time to see how it affects Days between, Days counting both dates and Whole years. The inputs you can vary are Start date, End date, Count the end date as a whole day and Holidays to exclude from business days.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate a month?
Days, weeks, months and years between two calendar dates, with the calendar breakdown, the business-day count and the weekday of each date; it also measures between two date-and-time instants. Open “How this is worked out” beside the result to see each step for your own figures.
Is this month 31 or 30?
Days, weeks, months and years between two calendar dates, with the calendar breakdown, the business-day count and the weekday of each date; it also measures between two date-and-time instants. Put your own figures in above and the working updates beside the result. For scale, the default figures on this page give 32 months.
What is 1 month in days?
Days, weeks, months and years between two calendar dates, with the calendar breakdown, the business-day count and the weekday of each date; it also measures between two date-and-time instants. On this page it is computed from Start date, End date and Count the end date as a whole day and shown as Days between, Days counting both dates and Whole years.
What information do I need for the Month Calculator?
You need Start date, End date, Count the end date as a whole day and Holidays to exclude from business days. The page opens with default figures that give whole months of 32 months, so you can see the scale before entering your own.
What does this Month Calculator show?
It shows Days between, Days counting both dates, Whole years, Extra months, Extra days, Extra hours, Extra minutes and Whole months, with the working and any warnings for your entries.
Can I check how the Month Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.