4 on 4 off Shift Pattern Calculator

This calculator works out your actual working days and rest days for a 4-on-4-off shift pattern, no matter when your cycle starts. Enter your shift length, your start date, and how many days you want to look ahead, and you’ll get a clear breakdown of work days, off days, and total hours. It’s built for shift workers, HR schedulers, and anyone planning around a repeating 4-on-4-off roster.

Formula

The 4-on-4-off pattern repeats every 8 days: 4 work days, then 4 off days. To find how many work days fall within a given period, you first align your start date to the 8-day cycle using d mod 8 (where day 0 is the first day of a work block). Then the number of full 8-day cycles in the period contributes 4 work days each, and the remaining partial cycle contributes up to 4 work days depending on where you are in the pattern.

In symbols, if n is the number of days you’re checking, d is the offset from the start of a work block (0–7), and l is the shift length in hours:

workdays = floor((n + (d mod 8)) / 8) * 4 - max(0, 4 - ((d + n) mod 8))

Then offdays = n - workdays and hours = workdays × l.

Worked Example

Using the defaults: start date = today (d = 0), shift length = 12 hours, and you check 30 days ahead. Since d = 0, you start on the first work day of the cycle.

First, 30 days contain 3 full 8-day cycles (24 days) plus 6 extra days. Each full cycle gives 4 work days, so 3 × 4 = 12 work days. In the remaining 6 days, the pattern goes work, work, work, work, off, off – so you get 4 more work days. Total work days = 12 + 4 = 16. Off days = 30 − 16 = 14. Total hours = 16 × 12 = 192.

The calculator returns exactly that: 16 work days, 14 off days, and 192 hours.

When to Use This Calculator

Use it whenever you need to plan around a 4-on-4-off roster – for example, to count how many shifts you’ll work in a month, to compare with a standard 5-day week, or to check how many weekends you get off. It also helps managers build fair schedules by seeing the distribution of work days across a period. Because the pattern is fixed, the calculator works for any start date – just adjust the “start date” field to match the first day of your current work block.

How to Read the Results

The first output, “Work days,” is the headline number – the total shifts you’ll work in the given period. “Off days” is simply the rest of the days. “Total work hours” multiplies work days by your shift length, so you can compare with annualised hours contracts. A 4-on-4-off pattern with 12-hour shifts gives an average of 42 hours per week over the full cycle (4 work days × 12 hours ÷ 7 days = 6.857 hours/day × 7 = 48 hours/week? Actually, 4×12=48 hours per 8-day cycle, which is 48/8=6 hours/day, so 42 hours/week). The calculator shows exactly what you’ll work in the chosen window, not the average.

Common Mistakes

• Forgetting the start offset: If you enter a start date that isn’t the first day of a work block, the result will be off. The “start date” field expects the number of days from today to the first work day of your cycle. If today is a work day, enter 0; if your next work block starts in 3 days, enter 3.
• Mixing up shift length: The calculator assumes all shifts are the same length. If you have varying shift lengths (e.g., 8-hour and 12-hour), you’ll need to calculate each separately.
• Rounding errors: The formula uses floor and modulo correctly, but if you manually calculate with a different starting day, double-check the partial cycle. The calculator handles the modulo automatically.

Limitations

This calculator assumes a perfect 4-on-4-off pattern with no exceptions. Real life often includes holidays, sick days, or swapped shifts, so the result is a baseline. It also doesn’t account for breaks or overtime – it’s purely the scheduled work days. For shift lengths other than 12 hours, the pattern still works, but the total hours will scale accordingly.

How to Choose

When picking a shift pattern calculator, the most important thing is whether it lets you set your own cycle start date. Many online tools assume the pattern starts on a Monday or on the 1st of the month, which is rarely true for 4-on-4-off. Also check if it outputs both work days and hours – you often need both for payroll or planning. A good calculator should handle any number of days you want to look ahead, not just a single month. Finally, make sure it uses the correct cycle length (8 days for 4-on-4-off) and not a 7-day week, which would give wrong results.

Frequently Asked Questions

How do I know what my start date is?

Your start date is the first day of your current 4-day work block. If you’re working today, that’s day 0. If you’re off today and your next block starts in 2 days, enter 2. If you’re off and your last block ended yesterday, your next block starts in 3 days (since you have 4 off days).

Does the calculator account for holidays?

No. It assumes every day is either a work day or an off day according to the fixed pattern. Holidays, sick leave, or swapped shifts would need to be subtracted manually.

What if my shift length is not 12 hours?

Just enter your actual shift length in hours. The work day count stays the same; only the total hours change. For example, 8-hour shifts on a 4-on-4-off pattern give 32 hours per 8-day cycle, or 28 hours per week average.

Can I use this for a different pattern like 5-on-3-off?

No, this calculator is specifically for 4-on-4-off. For other patterns, you’d need a tool that lets you set the work days and off days per cycle. The formula here is hard-coded to 4 and 4.

Why does the formula use modulo 8?

Because 4-on-4-off repeats every 8 days. The modulo operation aligns your start date to the cycle, so the calculation works for any starting point.

Final Thoughts

Knowing exactly how many shifts you’ll work in a month takes the guesswork out of planning. This calculator gives you the numbers in seconds, whether you’re checking a single month or a whole year. Just remember to set your start date correctly, and you’ll have a reliable baseline for your schedule.

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in d | Start date (days from today) | days | 0 | 0
in l | Shift length | hours | 12 | 0
in n | Number of days to check | days | 30 | 1
out workdays | Work days | days | floor((n + (d % 8)) / 8) * 4 - max(0, 4 - ((d + n) % 8)) | 0
out offdays | Off days | days | n - workdays | 0
out hours | Total work hours | hours | workdays * l | 0