How to Figure Out Which Dates You Work on a 24/48 or 48/96 Schedule (The Day-Count Method)

You are on a 24/48 rotation and someone asks, "Are you working the Saturday of the wedding?" The roster is at the station, the app is on the other phone, and you are standing in a parking lot.

You can answer from memory with arithmetic. This post shows a method for it: pick one shift date you are sure about, count the days to the date you want, divide by 3, and read the remainder. It works for a plain 24/48 and, with a small change, for a 48/96. All dates below are made up. It does not cover pay or overtime rules, only the counting. For how the rotations are built, see the firefighter schedules guide and the EMS schedules guide.

Why the count works

A 24/48 is one 24-hour shift followed by 48 hours off. That is a repeating cycle of 3 days: on, off, off. Three crews take turns, so every date belongs to exactly one crew, and your shift lands on every third date.

Any pattern that repeats every 3 days can be checked with remainders. If the number of days between your known shift and the target date divides evenly by 3, you are on duty that day.

The three steps

1. Anchor. Pick one date you are certain you work, from your own roster. Call it day 0.
2. Count. Count the days from the anchor to the target date. Later dates give a positive count; earlier dates give a negative count.
3. Divide by 3 and read the remainder.

A negative count works the same way once you take the positive remainder: a count of -2 is 1 more than -3, so the remainder is 1. In plain words, two days before an on-duty date, you are on your first day off.

Counting the days between dates

Inside one year, use the day number of the year. Days that have passed before the first of each month (non-leap year):

Add 1 to every month from March on in a leap year. The day number of a date is that figure plus the day of the month, so March 10 is 59 + 10 = 69. The count between two dates in the same year is the difference of their day numbers. Across a year boundary, add 365 days for each ordinary year you cross, or 366 for a leap year.

A worked example (made-up dates)

Suppose your roster says you work Friday, January 1, 2027. That is the anchor, day 0. Which of these do you work?

Thursday, November 25, 2027:

• Day number: 304 + 25 = 329. January 1 is day 1.
• Count from the anchor: 329 - 1 = 328 days.
• 328 ÷ 3 = 109 with a remainder of 1. 3 × 109 = 327, and 328 - 327 = 1.
• Remainder 1 means you are off. You worked the day before (November 24, count 327, remainder 0) and your next shift is 2 days later, November 27.

Wednesday, November 24, 2027: count 327, remainder 0, on duty. The count lines up with the day before, which is a good cross-check.

Wednesday, December 30, 2026 (before the anchor): count = -2. A shift on January 1 means the shift before it was 3 days earlier, December 29, so December 30 is the first day off. Remainder 1 under the rule above.

If you check one of these against your posted calendar and it does not match, your anchor is wrong or the schedule changed. Do not trust the arithmetic over the roster.

The same method on a 48/96

A 48/96 is two days on, four days off, a 6-day cycle. Anchor on the first day of one of your 48-hour tours (day 0) and divide the count by 6.

In the example above, the count to November 25 is 328. 328 ÷ 6 = 54 with a remainder of 4 (6 × 54 = 324). If January 1, 2027 were the first day of your 48, November 25 would be your third day off, with the next tour starting two days later, on November 27.

What the method does not know about

• Kelly days. Many departments drop an extra scheduled day off into the rotation every so often. The plain 3-day count breaks at that point and the shifts after it sit one day later (or the rhythm shifts) than the count says. Anchor on a shift after the most recent Kelly day, or check against the posted calendar. For how Kelly days are placed, see the Kelly day, explained.
• Trades and swaps. A traded shift changes who works the date, not the pattern. Keep your count on your own scheduled pattern. See shift trades explained.
• Different rotations. The method needs a pattern that repeats exactly. A rotation that changes over a longer cycle needs its full cycle length (the 4-on-4-off post shows an 8-day example).

Two things the day count also tells you

A year holds 121 or 122 shifts

The common figure for a 24/48 is a 56-hour week and 2,912 hours a year (56 × 52). A real year is 365 days, not 364, and 365 is not a multiple of 3: 3 × 121 = 363, which leaves 2 extra days.

So in a 365-day year, two of your three crews work 122 shifts (2,928 hours) and the third works 121 shifts (2,904 hours). In 2027 in the example, the crew that works January 1 or January 2 gets 122. The crew that starts on January 3 gets 121. A leap year has 366 days, which divides by 3 exactly, so every crew gets 122 (2,928 hours). The 3-year average is about 2,920 hours. The 2,912 figure is a handy approximation, not what any one year pays out.

Count your own year with the same method: list the dates with remainder 0, or divide the number of days in the year by 3 and see where your first shift falls.

A calendar week holds two shifts or three

Seven days is not a multiple of 3, so a Monday-to-Sunday week catches 2 shifts (48 hours) or 3 shifts (72 hours). Over three weeks (21 days) a crew works 7 shifts, which comes out to 3 + 2 + 2, or 72, 48 and 48 hours, in some order. Averaged out, that is 56 hours a week.

In the example, the weeks starting Monday January 4, 11 and 18, 2027 hold 3, 2 and 2 shifts. That repeating 72-hour week is one reason public fire agencies often count overtime over a longer work period rather than week by week. Under 29 CFR 553.230, the maximum hours standard for fire protection employees is 212 hours in a 28-day work period, or 53 in 7 days, and the rules for choosing that period are explained in the 7(k) post. Whether and how your agency uses it is a question for your payroll office or contract.

A quick checklist

1. Write down one shift date you are sure of (the anchor).
2. Count the days to the target date (day numbers inside a year; add 365 or 366 across years).
3. Divide by 3 for a 24/48, or by 6 for a 48/96, and read the remainder.
4. Compare with the roster for the Kelly day, trades and holiday rules.
5. Re-anchor after every Kelly day or schedule change.

Every date in this post is invented for illustration, and the method is general arithmetic, not a statement about any department's schedule. Your department's roster controls.

If you would rather see the whole year laid out than do the counting, Duty Pals, a shift calendar for Android, is on Google Play, and the shift pattern calculator on this site lists the working days and days off for 24/48, 48/96 and Kelly rotations from your start date.

Sources: 29 CFR 553.230 (212 hours in 28 days, 53 hours in 7 days) · all counts, remainders and totals are the author's own arithmetic on made-up dates, checked with a short script