3 on 3 off Shift Pattern Calculator

This calculator works out your average weekly hours and annual totals for a 3-on, 3-off shift pattern, where you work three days then have three days off. You enter your shift length and the number of cycles you work per year, and it returns your average weekly hours, annual work days, and annual hours. It’s built for nurses, factory workers, emergency services, and anyone whose roster follows this repeating cycle.

Formula

The core formula is simple: in a 3-on, 3-off pattern, you work 3 days out of every 6-day cycle. Your average weekly hours are calculated as:

Average weekly hours = (Shift hours × 3 work days × Cycles per year) ÷ 52 weeks

Where:

• Shift hours (h) – the length of one shift, usually 8, 10, or 12 hours.
• Cycles per year (c) – how many complete 6-day cycles you work in a year. Since a year has 365 days, the maximum is about 60.8 cycles (365 ÷ 6). Most people use 61 if they work every possible cycle.
• 52 – the number of weeks in a year.

The annual work days are simply 3 × cycles, and annual hours are shift hours × 3 × cycles.

Worked Example

Let’s use the default values: a 12-hour shift and 61 cycles per year.

• Average weekly hours = (12 × 3 × 61) ÷ 52 = 2196 ÷ 52 = 42.2 hours
• Annual work days = 3 × 61 = 183 days
• Annual work hours = 12 × 3 × 61 = 2196 hours

So with 12-hour shifts and 61 cycles, you work about 42.2 hours per week on average, 183 days per year, and 2196 hours per year.

When to Use This Calculator

Use this tool when you’re evaluating a job offer, planning your yearly schedule, or comparing different shift lengths. It’s particularly useful for:

• Checking if your average weekly hours exceed a full-time threshold (often 40 hours).
• Estimating your annual leave entitlement if your employer calculates it based on hours worked.
• Comparing a 3-on/3-off pattern with a standard Monday–Friday job.

The result is an average; some weeks will have more work days (e.g., 4) and some fewer (e.g., 2), but the average over a year is stable.

How to Read the Result

The average weekly hours tells you the typical workload across the year. For example, 42.2 hours per week is slightly above a standard 40-hour week, meaning you’d accrue overtime or additional pay if your contract is based on 40 hours. The annual work days (183) is roughly 50% of the year, which is typical for this pattern. The annual hours (2196) is the total you’d work if you take no unpaid leave.

Common Mistakes

• Using 52.18 weeks – Some calculators use 52.18 (365.25/7) for more precision, but the difference is tiny (less than 0.5%). Stick with 52 for simplicity.
• Forgetting to account for leave – This calculator assumes you work every cycle. If you have paid annual leave, you’ll actually work fewer cycles. Subtract your leave weeks from the cycles per year.
• Mixing up cycles and weeks – A cycle is 6 days, not a week. Don’t enter 52 as cycles; that would mean 312 work days, which is impossible.

Limits of the Formula

This formula assumes a perfectly repeating 3-on/3-off pattern with no holidays, sick days, or shift swaps. Real rosters often have exceptions. Also, it doesn’t account for night shifts, which might have different pay rates or rest requirements. Always check your actual contract for how overtime and leave are calculated.

Frequently Asked Questions

How many cycles are there in a year?

There are 365 days in a common year, so 365 ÷ 6 = 60.83 cycles. Most people round up to 61, but if you have paid leave, you’ll work fewer. For example, if you take 4 weeks of leave, that’s about 4.67 cycles, so you’d work about 56 cycles.

Is 3-on/3-off considered full-time?

It depends on your shift length. With 12-hour shifts, the average is 42.2 hours per week, which is full-time in most places. With 8-hour shifts, it’s only 28.2 hours per week, which is part-time. Check your local labor laws or your contract.

How many days off do I get per year?

In a 3-on/3-off pattern, you have 3 days off per 6-day cycle, so roughly half the year. With 61 cycles, that’s 183 days off (365 – 183). This includes weekends and weekdays mixed.

Can I use this for a 4-on/4-off pattern?

No, this calculator is specific to 3-on/3-off. For a 4-on/4-off pattern, you’d work 4 days out of 8, so the formula would be (shift hours × 4 × cycles) ÷ 52, with cycles = 365 ÷ 8 ≈ 45.6.

Does this calculator account for public holidays?

No. Public holidays are not automatically included. If you work on a public holiday, you might get extra pay or a day off in lieu, but that’s not part of this calculation. Adjust your cycles per year if you have fixed holidays off.

Final Thoughts

The 3-on/3-off pattern is popular in 24/7 industries because it provides predictable blocks of time off. This calculator gives you a quick, accurate snapshot of your annual workload, helping you plan finances, leave, and personal projects. Just remember to adjust the cycles per year for any unpaid leave or holidays you know you’ll take.

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in h | Shift length (hours) | h | 12 | 0
in c | Cycles per year | - | 61 | 0
out weekly | Average weekly hours | h | (h * 3 * c) / 52 | 1
out days | Annual work days | days | 3 * c | 0
out annual | Annual work hours | h | h * 3 * c | 0