Shift Pattern Calculator: How to Work It Out

A shift pattern calculator works out your total working hours and average hours per week from a repeating roster, so you can see at a glance whether a schedule meets your contract or your needs. You enter the pattern length, the shift lengths, and the number of rest days, and it returns the average weekly hours and the total hours per cycle. This lets you compare different rosters before committing to one.

Formula

The core formula is simple: Average weekly hours = (Shift length × Work days per pattern) ÷ (Pattern length ÷ 7). In symbols:

Avg = (S × W) / (T / 7)

Where:

• S = shift length in hours (e.g., 8 for a standard day shift, 12 for a 12-hour shift)
• W = number of work days in one full pattern cycle
• T = total length of the pattern in days (e.g., 14 for a two-week roster, 28 for a four-week roster)

The result is the average hours per week over the whole cycle. The total hours per pattern is simply S × W.

Worked Example

Using the default values from the calculator above: a 14-day pattern, 8-hour shifts, and 10 work days.

1. Total hours per pattern = 8 × 10 = 80 hours
2. Number of weeks in the pattern = 14 ÷ 7 = 2 weeks
3. Average weekly hours = 80 ÷ 2 = 40.00 hours per week

The calculator shows 40.00 h/week and 80.0 hours total for the pattern, matching the manual calculation.

Why Calculate Shift Patterns?

Shift workers often face rosters that are anything but a standard Monday–Friday schedule. A pattern might be “4 on, 4 off” with 12-hour shifts, or a rotating cycle of mornings, afternoons, and nights. Manually adding up hours across a month is error-prone, especially when the pattern length doesn’t divide neatly into weeks. A calculator removes that guesswork, giving you a single number—average weekly hours—that you can compare against a contract, a job posting, or a legal limit.

It also helps in planning. If you know a pattern averages 42 hours per week, you can estimate monthly earnings (if you know the hourly rate) or decide whether the overtime is worth the fatigue. For employers, it helps design rosters that stay within agreed working time limits.

How to Use the Calculator

You need three pieces of information from your roster:

• Pattern length – the number of days in one full cycle. Common values: 7, 14, 21, 28.
• Shift length – the number of hours you work per shift. This includes paid breaks if you want total paid hours, or excludes them if you want actual working time.
• Work days per pattern – how many of those days you actually work. Rest days are the difference.

Enter those three numbers, and the calculator returns the average weekly hours and the total hours for the whole pattern. If your pattern has different shift lengths (e.g., some 8-hour and some 12-hour days), you’ll need to calculate the weighted average shift length first, then use that as the “shift length” input.

Common Mistakes and Misconceptions

The most frequent error is mixing up pattern length and work days. A 14-day pattern with 10 work days is not the same as a 10-day pattern. Always count the full cycle from the first day of one pattern to the last day before it repeats.

Another common mistake is forgetting that a “week” is 7 days, not 5. If you divide total hours by 5 (thinking of a working week), you’ll get an inflated average. The formula above uses 7 because the pattern length is measured in calendar days.

A related misconception: a 4-on, 4-off schedule with 12-hour shifts does not average 42 hours per week. Let’s check: pattern length = 8 days, work days = 4, shift = 12. Total hours = 48. Weeks = 8/7 = 1.143. Average = 48 / 1.143 = 42.0 hours. So it does average 42 hours per week—but many people assume it’s 48 because they only look at the 4 work days. The calculator catches that.

Limitations of the Formula

This calculator assumes every shift is the same length and that the pattern repeats exactly. Real rosters often have variations:

• Different shift lengths on different days (e.g., 8-hour days and 12-hour nights)
• Unpaid breaks that reduce paid hours
• Overtime that isn’t part of the regular pattern
• Public holidays that fall on work days and change the actual hours worked

For those cases, you’ll need to adjust the inputs. For example, if you have a mix of 8-hour and 12-hour shifts, calculate the average shift length weighted by how often each occurs, then use that as the shift length. If breaks are unpaid, subtract them from the shift length before entering it.

The result is an average, not a guarantee. A pattern that averages 40 hours per week might have one week at 48 hours and another at 32. That’s fine for planning, but if you need to know exact weekly hours for payroll or legal compliance, you should count each week individually.

Alternatives to a Manual Calculator

If you don’t want to use this online tool, you can do the math by hand with the formula above. A spreadsheet also works well: put pattern length, shift length, and work days in separate cells, then write the formula = (shift_length * work_days) / (pattern_length / 7). That gives you a reusable template for comparing many rosters.

Some shift workers prefer to count total hours per month instead of per week. To convert, multiply the weekly average by 4.33 (the average number of weeks in a month). For the example above, 40 hours/week × 4.33 = 173.2 hours per month.

If your roster is irregular and doesn’t repeat, no simple calculator will work. In that case, list each shift’s hours and add them up, then divide by the number of weeks in the period you’re interested in.

Frequently Asked Questions

What is a typical shift pattern length?

Common patterns are 7 days (weekly), 14 days (two weeks), 21 days (three weeks), and 28 days (four weeks). Some industries use 8-day cycles (like 4-on/4-off) or 10-day cycles. The calculator works for any length, as long as you enter the full cycle.

How do I handle a pattern with both 8-hour and 12-hour shifts?

Calculate the weighted average shift length. For example, if a 14-day pattern has 6 days of 8 hours and 4 days of 12 hours, total work hours = (6×8) + (4×12) = 48 + 48 = 96 hours. Work days = 10. Average shift length = 96 ÷ 10 = 9.6 hours. Enter 9.6 as the shift length and 10 as the work days.

Does this calculator include breaks?

No, it uses whatever you enter as the shift length. If you want paid hours, enter the shift length including paid breaks. If you want actual working time, enter the shift length minus unpaid breaks. For example, a 9-hour shift with a 1-hour unpaid break should be entered as 8 hours.

What if my pattern doesn’t repeat?

Then the concept of a “pattern” doesn’t apply. You’ll need to add up all hours over a specific period (say, a month) and divide by the number of weeks in that period to get an average. This calculator is for repeating rosters only.

How many hours is a full-time shift pattern?

That depends on your country and contract. In many places, full-time is around 35–40 hours per week. The calculator doesn’t judge whether a pattern is full-time or part-time; it just gives you the average so you can compare it to your own definition.

Can I use this for a 24/7 rotating schedule?

Yes, as long as the rotation repeats. For example, a 4-week cycle with 4 days on, 2 days off, 4 nights on, 2 days off, etc., would have a pattern length of 28 days. Count the work days (including nights) and use the average shift length (often 12 hours for night shifts). The calculator will give you the weekly average.

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in t | Pattern length | days | 14 | 7
in s | Shift length | hours | 8 | 1
in w | Work days per pattern | days | 10 | 1
out avg | Average weekly hours | h/week | (s * w) / (t / 7) | 2
out total | Total hours per pattern | hours | s * w | 1