How Many Vacation Shifts Does a Week Off Cost on a 24/48 or 48/96 Schedule? (How to Calculate Leave Hours)

A firefighter on a 24/48 rotation asks for "a week off in March." The roster says that costs three shifts, a coworker says it costs two, and both are right. The difference is not the department. It is the day the week starts.

This post is about counting leave on a 24-hour rotation. It uses invented numbers and one habit: count the shifts you are scheduled to work inside the dates, not the days on the calendar. It does not cover how leave accrues (that is the PTO accrual in hours post), whether leave counts toward overtime (that is the PTO and overtime post), or how the schedules themselves are built (that is the firefighter shift schedules guide).

Step 1: Count shifts, not days

On a 24/48 you work one calendar day, then are off for two, so you are on duty one day in every three. Any run of consecutive calendar days therefore contains about one third as many shifts as days. "About" is the whole story, so here it is exactly.

Take a window of days and call the first day of the window day 0. Your first shift inside the window falls on day 0, day 1, or day 2. Call that number f. Your shifts then land on f, f+3, f+6, and so on, as long as they are inside the window.

Take a 7-day window (days 0 to 6):

• f = 0: shifts on days 0, 3, 6, which is 3 shifts.
• f = 1: shifts on days 1, 4 (day 7 is outside), which is 2 shifts.
• f = 2: shifts on days 2, 5 (day 8 is outside), which is 2 shifts.

Check: (3 + 2 + 2) ÷ 3 = 2.33 shifts, and 7 ÷ 3 = 2.33. The average matches, so the counting is right.

A 14-day window (days 0 to 13):

• f = 0: days 0, 3, 6, 9, 12 is 5 shifts.
• f = 1: days 1, 4, 7, 10, 13 is 5 shifts.
• f = 2: days 2, 5, 8, 11 (day 14 is outside) is 4 shifts.

Check: (5 + 5 + 4) ÷ 3 = 4.67 shifts, and 14 ÷ 3 = 4.67.

Step 2: Turn shifts into leave hours

Multiply by the number of hours your department charges per shift of leave. Many departments charge the full 24. Some charge a different number, so this is a policy question, not arithmetic. This post assumes 24 for the examples.

Arithmetic check: 2 × 24 = 48, 3 × 24 = 72, 4 × 24 = 96, 5 × 24 = 120, 7 × 24 = 168. For a 10-day window: f = 0 gives days 0, 3, 6, 9 (4 shifts); f = 1 gives days 1, 4, 7 (3 shifts); f = 2 gives days 2, 5, 8 (3 shifts). For 21 days, 21 is a multiple of 3, so every start day gives exactly 7.

Windows whose length is a multiple of 3 (6, 9, 12, 15, 21 days) never vary. Windows that are one or two days over a multiple of 3 (7, 10, 14 days) can cost one extra shift, which is 24 hours of leave, for nothing but the starting date.

Step 3: A worked example with a made-up balance

Say you have 120 hours of vacation banked, and you want two weeks (14 days) off.

• If the 14 days start so your first shift is on day 0 or day 1, it costs 5 shifts, or 5 × 24 = 120 hours. Your balance is now 120 − 120 = 0.
• If it starts so your first shift is on day 2, it costs 4 shifts, or 4 × 24 = 96 hours. Your balance is 120 − 96 = 24.

Same two weeks on the calendar, a 24-hour difference. At a made-up $30 an hour, 24 hours is 24 × 30 = $720 of leave value.

Step 4: How many days away does each shift of leave buy?

There is a better question than "how many shifts is a week." It is "how many days am I away from work for each shift of leave?" Because you are already off before and after a leave shift, the answer is more than the shift itself.

Start the clock the morning you are relieved from your last shift. Take n consecutive shifts of leave, and come back on the next shift after that.

On a 24/48 you are away for n shift days, plus a 2-day off block before the first, plus a 2-day block after each one. That is n + 2(n + 1) = 3n + 2 days.

Check: 3 × 4 + 2 = 14, and 3 × 5 + 2 = 17. This is where the 4-shift, 14-day case above comes from: it works when the window starts the morning after one of your shifts and ends the day before your next.

The same logic on a 48/96 (48 hours on, 96 hours off, a 6-day cycle). Each tour is 2 calendar days and the off blocks are 4 days. For n tours of leave, you are away 2n + 4(n + 1) = 6n + 4 days.

Check: 6 × 1 + 4 = 10, 6 × 2 + 4 = 16, 6 × 3 + 4 = 22.

Look at the pattern in both tables. Each extra 24 hours of leave buys 3 more days on 24/48 (so 8 hours of leave per day away), and each extra 48 hours of leave buys 6 more days on 48/96 (also 8 hours per day away). The rotation's off blocks are the free part: 4 bonus days on 24/48 and 8 on 48/96, counting both sides. That is the arithmetic behind the common advice to plan a long break around the rotation instead of around a Monday.

Not every department lets you take half of a 48-hour tour as leave, or charges the same hours for it. Where it does not, the 48/96 numbers above are the only clean ones.

Step 5: What the law does and does not say

• Federal law does not set how many hours a department charges for a leave shift. That comes from your pay policy or contract.
• 29 CFR § 778.218 covers payments for occasional periods when an employee is not at work because of vacation, holiday or illness, and says that no part of such payments may be credited toward overtime compensation due under the Act. Whether a leave shift counts toward your department's overtime threshold is a separate question for your local policy; see the PTO and overtime post and, for how the overtime threshold itself works, the Kelly day post.

Step 6: A checklist before you request the dates

1. Count shifts inside your dates, using your own roster, not days ÷ 3.
2. Find your f. On which day of the window is your first shift: day 0, 1 or 2?
3. Slide the start date by a day or two and recount. A 7- or 14-day window can change by one shift.
4. Multiply by what your department charges per shift, which may not be 24.
5. Compare with your balance in hours, not days.
6. Ask whether a shift you trade away still gets charged, and whether a Kelly day inside the window changes the count.

Every figure here is invented for illustration. This is general information, not legal or pay advice. Your department's leave policy or collective bargaining agreement controls how leave is counted and charged, and your payroll office can confirm it.

If you plan time off against a rotation, seeing the shifts laid out on real dates makes the count easy. Duty Pals, a shift calendar for Android, is on Google Play, and the shift pattern calculator on this site covers 24/48 and 48/96.

Sources: 29 CFR 778.218 · counts are the author's own arithmetic on a repeating pattern