Why a month of service counts as 30 days — and when it changes the result
Published: 15 September 2026 · Izračunaj.ba
When work tenure is calculated, a month is not a number of calendar days but a unit: every full calendar month counts as 30 days, whether it has 28 or 31, and both the first and the last day count. That is why 1 to 28 February 2025 is a full month of service, while the same dates in 2024, when February has 29 days, give 28 days. Days only matter in incomplete months and are added up across all periods: 30 days become a month and 12 months a year.
The rule: a month is a unit, not a number of days
days = last day − first day + 1 (both count)30 days = 1 month12 months = 1 year
The calendar counts days; tenure counts months. For every employment period both the first and the last day count, the 31st of a month and the last day of February stand for the 30th, and every full calendar month is exactly 30 days. Days are then added up across all periods: 30 of them become a month, and 12 months become a year.
The cleanest example is a whole calendar year. From 1 January to 31 December 2025, 365 days pass and the tenure is exactly 1 year. The date difference calculator shows 11 months and 30 days for the same pair of dates, because it measures the gap between two dates rather than days worked — the last day is not part of that gap.
This is the convention the work tenure calculator uses. Official tenure is determined by the pension fund based on registrations and paid contributions, so for your pension its decision is what counts.
Work experience calculatorTotal tenure across multiple employment periods.Open the calculator →A full month is 30 days — whether it has 28 or 31
The table lists periods that cover whole months. The number of calendar days runs from 28 to 31, yet the tenure is the same every time: one month. January is already full on 30 January — the 31st adds nothing, because it also stands for the 30th.
February is the only month where a leap year changes the outcome. 1 to 28 February 2025 is a full month, because the 28th was the last day of that February. The same dates in 2024 give 28 days, because that February also had a 29th — only the period up to 29 February 2024 becomes a month.
The same holds for longer periods: 1 June to 31 August 2025 spans 92 calendar days, 1 January to 31 March only 90, and both are exactly 3 months of service.
| Period | Calendar days | Tenure |
|---|---|---|
| 1 Jan – 30 Jan 2025 | 30 | 1 month |
| 1 Jan – 31 Jan 2025 | 31 | 1 month |
| 1 Feb – 28 Feb 2025 | 28 | 1 month |
| 1 Feb – 28 Feb 2024 | 28 | 28 days |
| 1 Feb – 29 Feb 2024 | 29 | 1 month |
| 1 Jan – 31 Mar 2025 | 90 | 3 months |
| 1 Jun – 31 Aug 2025 | 92 | 3 months |
Short periods: where a day is gained and where it is lost
When a period does not cover a whole month, days are counted — but the end of the month still stands for the 30th. That makes a difference precisely for short jobs that end at the end of a month.
A job from 10 to 28 February 2025 lasts 19 calendar days but brings 21 days of tenure: the last day of February counts as the 30th, so the days from the 10th to the 30th are counted. A job from 10 to 31 January lasts 22 calendar days and also brings 21 days, because the 31st is not counted separately. If the same job ends on 30 January, the tenure is again 21 days.
Periods that do not touch the end of a month hold no surprises: 10 to 25 January spans 16 calendar days, and that is 16 days of tenure.
| Period | Calendar days | Tenure |
|---|---|---|
| 10 Jan – 25 Jan 2025 | 16 | 16 days |
| 10 Jan – 30 Jan 2025 | 21 | 21 days |
| 10 Jan – 31 Jan 2025 | 22 | 21 days |
| 10 Feb – 28 Feb 2025 | 19 | 21 days |
One job in two parts: when a split adds a day
The period from 1 January to 31 March 2025 is exactly 3 months of tenure. If the same job is recorded as two periods, the result depends on where the cut is.
A cut at the end of January changes nothing: 1 to 31 January is 1 month, 1 February to 31 March is 2 months, 3 months in total. A cut between 30 and 31 January adds a day: the period up to 30 January is already a full month, and the period starting on 31 January starts from “the 30th” and brings 2 months and 1 day. The total is 3 months and 1 day — one day more than for uninterrupted work.
A cut in the middle of a month, on the other hand, cancels out. A job from 3 March 2014 to 17 September 2019 and the next one from 18 September 2019 to 31 August 2026 together give 12 years, 5 months and 28 days — exactly as much as one uninterrupted period from 3 March 2014 to 31 August 2026.
If you compare your total with the records and see a difference of a day or two, first look at periods that start or end on the 30th or 31st of a month or at the end of February — that is where the convention departs most from the calendar.
Several periods and overlaps
Days from different periods are added up. Two short jobs, from 10 to 25 January (16 days) and from 5 to 24 March 2025 (20 days), together give 1 month and 6 days of tenure: 36 days, 30 of which become a month.
When two periods overlap — say a permanent job throughout 2020 and secondary work from 1 June to 31 August of the same year — the calculator adds both, shows 1 year and 3 months and warns about the overlap. For pension purposes, overlapping time generally does not count twice, so check with the pension fund what is recognized.
Tenure or date difference?
The work tenure calculator answers “how long did I work”: it counts both end days and months of 30 days. The date difference calculator answers “how much time is there between two dates”: it uses real month lengths and does not count the last day.
For the first three months of 2025 the date difference is 2 months and 30 days, or 89 days, while the tenure is exactly 3 months. Neither number is wrong — they measure different things. Use the date difference for deadlines and days until an event, and tenure for years of work.
Check the example in the calculator
The example with the cut between 30 and 31 January opens with both periods already filled in, and the result is 3 months and 1 day. Change the end of the first period to 31 January and the start of the second to 1 February, and the tenure goes back to exactly 3 months.