How to Calculate a Semi-Monthly Timesheet
Split the pay period into its workweeks, including any week that starts before the 1st or 16th or ends after the 15th or month-end. Total each workweek in hours and minutes, take overtime only above 40 in a week, then add the hours that fall inside the period. Never apply an 86:40 or 80-hour threshold to the period.
What is a semi-monthly pay period?
Semi-monthly means twice a month on fixed dates. The usual split is the 1st to the 15th and the 16th to the last day of the month, which gives 24 pay periods a year. Some employers use other dates, such as the 6th to the 20th, but the arithmetic is the same.
The first half of a month is always 15 days. The second half is 13 to 16 days, depending on the month. And because the dates are tied to the calendar rather than to the days of the week, a semi-monthly period almost never starts on the first day of a workweek or ends on the last.
That is the whole difficulty. Total hours for the period are easy. Overtime is not, because overtime belongs to the workweek, and a semi-monthly period usually cuts a workweek in two at each end.
How many hours are in a semi-monthly pay period?
The figure you’ll see quoted is 86:40, or 86.67 decimal hours. It comes from a 2,080-hour full-time year: 2,080 ÷ 24 = 86.67, and 0.67 of an hour is 40 minutes.
That is an average, not what lands on any real timesheet. Count the weekdays in each half-month and the scheduled hours swing by a full three days. Here is 2027 on a Monday-to-Friday, eight-hour schedule, before holidays:
| 2027 | 1st–15th | 16th–end |
|---|---|---|
| January | 11 days · 88:00 | 10 days · 80:00 |
| February | 11 days · 88:00 | 9 days · 72:00 |
| March | 11 days · 88:00 | 12 days · 96:00 |
| April | 11 days · 88:00 | 11 days · 88:00 |
| May | 10 days · 80:00 | 11 days · 88:00 |
| June | 11 days · 88:00 | 11 days · 88:00 |
| July | 11 days · 88:00 | 11 days · 88:00 |
| August | 10 days · 80:00 | 12 days · 96:00 |
| September | 11 days · 88:00 | 11 days · 88:00 |
| October | 11 days · 88:00 | 10 days · 80:00 |
| November | 11 days · 88:00 | 11 days · 88:00 |
| December | 11 days · 88:00 | 12 days · 96:00 |
The 24 periods hold 261 weekdays in all, which is 2,088 scheduled hours rather than 2,080 — the same gap explained in how many work hours are in a year. An hourly worker on a fixed schedule should expect a timesheet anywhere from 72:00 to 96:00, and neither end means anything is wrong.
How do I calculate a semi-monthly timesheet?
Work by workweek first and by pay period last. These six steps handle every split:
- Write down your workweek. Your employer sets a fixed, recurring seven-day workweek — often Sunday 12:00 AM to Saturday 11:59 PM. Your handbook or pay stub usually says which.
- Map every day of the period to its workweek. For December 1–15, 2026, with a Sunday start, that is three weeks: Nov 29–Dec 5, Dec 6–12 and Dec 13–19. Only the middle one is wholly inside the period.
- Total each workweek in H:MM, including the days that sit in the neighboring pay period. Add hours and minutes as hours and minutes; never type
8:45as8.45. - Find each week’s overtime — anything over
40:00— and place it on the last hours worked that week. That decides which pay period it belongs to. - Hold open weeks until they close. If the period ends mid-week, pay the hours worked so far as regular time. That week’s overtime, if any, is settled in the next period once the week is complete.
- Add the period’s regular and overtime hours separately, convert each to decimal, and multiply by the rates.
A worked example: December 1–15, 2026
An hourly worker paid $20.00 an hour, time-and-a-half over 40 hours a week, with a Sunday-to-Saturday workweek. Weekends off. The hours below are net of unpaid breaks.
Week A: Sunday, November 29 to Saturday, December 5
This week starts in the previous pay period. Monday, November 30 was already paid on the November 16–30 timesheet.
| Day | Pay period | Hours | Week so far |
|---|---|---|---|
| Mon Nov 30 | Nov 16–30 | 9:15 | 9:15 |
| Tue Dec 1 | Dec 1–15 | 8:30 | 17:45 |
| Wed Dec 2 | Dec 1–15 | 9:00 | 26:45 |
| Thu Dec 3 | Dec 1–15 | 8:45 | 35:30 |
| Fri Dec 4 | Dec 1–15 | 8:00 | 43:30 |
The week is 43:30, so it holds 3:30 of overtime. The week crossed 40 hours on Friday, after 4:30 of that day’s eight hours, so the last 3:30 of Friday is the overtime — and Friday is in the December 1–15 period.
December’s share of week A is 8:30 + 9:00 + 8:45 + 8:00 = 34:15, which splits into 30:45 regular and 3:30 overtime. Check it: November’s 9:15 plus December’s 30:45 is exactly 40:00 of regular time for the week.
Week B: Sunday, December 6 to Saturday, December 12
Wholly inside the period: 8:00 + 8:30 + 8:00 + 8:15 + 8:00 = 40:45. That is 40:00 regular and 0:45 overtime.
Week C: Sunday, December 13 to Saturday, December 19
Only Monday and Tuesday are in this period: 8:30 + 8:45 = 17:15. The week is still open when the period closes on the 15th, so those 17:15 are paid as regular time for now.
The December 1–15 total
| Workweek | Hours in period | Regular | Overtime |
|---|---|---|---|
| A · Nov 29–Dec 5 | 34:15 | 30:45 | 3:30 |
| B · Dec 6–12 | 40:45 | 40:00 | 0:45 |
| C · Dec 13–19 (open) | 17:15 | 17:15 | 0:00 |
| Period | 92:15 | 88:00 | 4:15 |
In decimal, 88:00 is 88.00 hours and 4:15 is 4 + 15÷60 = 4.25 hours. The pay:
- Regular:
88.00 × $20.00 = $1,760.00 - Overtime:
4.25 × $30.00 = $127.50 - Gross for the period: $1,887.50
Then week C finishes in the next period: Wednesday 8:00, Thursday 8:30, Friday 8:15, another 24:45. The full week is 17:15 + 24:45 = 42:00, so it has 2:00 of overtime, all of it on Friday, December 18. The December 16–31 timesheet carries week C as 22:45 regular and 2:00 overtime — and 17:15 + 22:45 is, again, exactly 40:00 of regular time.
Why not just count overtime over 86:40?
Because the pay period isn’t the unit overtime is measured in, and a period threshold is wrong in both directions. Run the same December period three ways:
| Method | Overtime hours | Gross at $20/hr | vs correct |
|---|---|---|---|
| Per workweek, straddling weeks included | 4:15 | $1,887.50 | — |
| Everything over 86:40 in the period | 5:35 | $1,900.83 | $13.33 over |
| Only weeks wholly inside the period | 0:45 | $1,852.50 | $35.00 short |
The 86:40 method looks generous here. In a short period it does the opposite. Take February 16–28, 2027, scheduled at 72:00. A worker does five eight-hour days in the week of February 14–20 — exactly 40:00, with Monday the 15th in the previous period and 32:00 in this one — and then a 45-hour week from February 21–27. The period is 32:00 + 45:00 = 77:00 — nowhere near 86:40 — so the threshold method pays no overtime. But the second week holds 5:00 of it, worth 5 × $10.00 = $50.00 in premium at $20 an hour: $1,590.00 owed, not $1,540.00.
The “whole weeks only” mistake is the quieter one. It produces a tidy timesheet and loses the overtime from every week that straddles a cutoff, which on a semi-monthly calendar is most of them.
What if my semi-monthly period ends in the middle of a week?
It usually will. The hours worked up to the cutoff are paid on that period’s timesheet, as regular time unless the week has already passed 40 hours. Once the week ends, the full week is totaled and any overtime is paid. Federal guidance generally expects overtime to be paid on the regular payday for the period in which the workweek ends, or as soon as practicable after that if it can’t be worked out in time.
The one case that catches people: a week that has already crossed 40 hours before the cutoff. If week C above had been three 14-hour days — Sunday the 13th through Tuesday the 15th — it would already sit at 42:00 by the cutoff, and those 2:00 of overtime belong on the December 1–15 timesheet, not the next one.
How do I check a semi-monthly paycheck?
Rebuild it the same way, then compare line by line:
- The regular hours on the stub should equal your in-period hours minus the overtime you placed in this period —
88:00above, shown as 88.00. - The overtime hours should include the tail of any straddling week that ended inside the period —
4:15above, shown as 4.25. - An open week at the end should show only regular time, and you should see its overtime on the next stub.
- Stub hours are decimal.
92.25is92:15, not 92 hours 25 minutes.
How to check if your paycheck is correct goes through the full comparison, and how to calculate a biweekly timesheet covers the simpler case where every period holds two whole weeks.
What are the common semi-monthly timesheet mistakes?
- Using a biweekly threshold. 80 hours means nothing on a semi-monthly timesheet; neither does 86:40.
- Dropping the straddling days. Monday, November 30 isn’t on the December timesheet, but it is in week A, and without it week A looks like
34:15with no overtime. - Assuming every period is the same length. A 96:00 period isn’t overtime and a 72:00 period isn’t a short-pay error, on a normal schedule.
- Adding clock digits as decimals. Typing week A’s December days as
8.30 + 9.00 + 8.45 + 8.00gives 33.75 instead of 34.25 — half an hour lost in one week. - Expecting overtime by the day or by the period. The federal rule is weekly. Some states and contracts add daily overtime, which is a separate calculation on top.
Total each week in seconds
Hours adds time as time, so 9:15 + 8:30 + 9:00 + 8:45 + 8:00 comes out as 43:30 on the spot — you can see the overtime before the pay period even closes. One tap shows 92.25 decimal hours, your hourly rate turns hours into pay, and saved history exports to CSV or PDF for a clean record of each week. Free, offline, no ads, no tracking, no sign-in.
Frequently asked questions
What is a semi-monthly timesheet?
A timesheet for a pay period that runs twice a month on fixed dates, usually the 1st–15th and the 16th–end. There are 24 a year, each 13 to 16 days long.
How many hours are in a semi-monthly pay period?
86:40 (86.67 hours) on average. On a Monday-to-Friday, eight-hour schedule in 2027 the real periods run from 72:00 to 96:00 before holidays.
How is overtime calculated on a semi-monthly payroll?
Per workweek. Hours over 40 in your employer’s fixed seven-day week are overtime; the pay period has no threshold of its own.
What happens to overtime when a workweek is split between two pay periods?
Total the whole week across both periods. The overtime sits on the last hours worked, so it usually lands in the period that holds the end of the week. An open week is paid as regular time until it closes.
Is semi-monthly the same as biweekly?
No. Biweekly is 26 periods of exactly 14 days, each holding two whole workweeks. Semi-monthly is 24 periods of 13 to 16 days that usually split a week at each end.
How do I convert a semi-monthly total to decimal hours?
Divide the minutes by 60: 92:15 is 92.25 hours and 86:40 is 86.67. Never read 92:15 as 92.15.
Overtime and pay-timing practices described here are general United States information, not legal or tax advice. Your state, contract, collective agreement or employer policy may set different rules, including daily overtime — check your handbook, your employer, or a qualified adviser.