Why is 1.30 the line?

It is Capillary's default high-burden line, about 30% more risk than a first 8-hour day shift. A first 12-hour day shift scores 1.28, just under it, and a first 12-hour night 1.34. You can change the line in Analytics.

How is this different from the alertness calculator?

This one scores injury risk from shift features; the shift alertness calculator predicts alertness from sleep and the body clock. They can disagree: a 12-hour night from 19:00 and an 8-hour night from 23:00 reach the same predicted low near 05:45, but this calculator scores them 1.34 and 1.06.

Is anything I enter sent or saved?

No. The calculator runs in your browser and sends nothing.

Shift fatigue risk calculator

Updated October 8, 2026 · 2 min read · free calculator

This calculator scores each shift in a run of up to 7 days against a first 8-hour day shift (1.00). It adds the parts of a 2006 injury-risk index, as the paper's formula does: the first shift of its type, its place in the run and its length, and marks any shift at 1.30 or more.

Score your shifts

Calculator · runs in your browser, nothing is sent

Day 1Day 1 shiftDay 1 hoursh
1.34
1.06 + 0.00 + 0.275
Day 2Day 2 shiftDay 2 hoursh
1.40
1.06 + 0.06 + 0.275
Day 3Day 3 shiftDay 3 hoursh
1.51
1.06 + 0.17 + 0.275
Day 4Day 4 shiftDay 4 hoursh
1.70
1.06 + 0.36 + 0.275
Day 5Day 5 shiftDay 5 hoursh
Day off: the run starts again
Day 6Day 6 shiftDay 6 hoursh
Day off: the run starts again
Day 7Day 7 shiftDay 7 hoursh
1.13
1.00 + 0.00 + 0.13

Relative risk = first shift of its type + its place in the run + its length, added as in the 2006 paper, against a first 8-hour day shift (1.00). Red marks 1.30 or more, the default high-burden line for the risk index in Capillary's Analytics.

For each day, choose off, morning or day, afternoon or evening, or night, and enter the shift length in hours. The example starts with four 12-hour nights, then two days off and a 10-hour day shift.

What it adds

Parts of the score (1.00 = a first 8-hour day shift)
Part	Values
First shift of its type	Morning or day 1.00; afternoon or evening 1.03; night 1.06
Nights in a row	1st +0.00; 2nd +0.06; 3rd +0.17; 4th +0.36; then +0.119 a night
Other shifts in a row	1st +0.00; 2nd +0.02; 3rd +0.07; 4th +0.17; then +0.056 a day
Shift length	8 h or less +0.00; 10 h +0.13; 12 h or more +0.275; a straight line between

The night, run and length values are the 2006 paper's own; the evening value sits between day and night, following the paper's three-shift trend. A day off restarts the run. For the research behind each part, see the fatigue risk index guide.

Worked example

The example run, scored
Day	Shift	Calculation	Score
1	Night, 12 h	1.06 + 0.00 + 0.275	1.34
2	Night, 12 h	1.06 + 0.06 + 0.275	1.40
3	Night, 12 h	1.06 + 0.17 + 0.275	1.51
4	Night, 12 h	1.06 + 0.36 + 0.275	1.70
5 and 6	Off	None	The run restarts
7	Day, 10 h	1.00 + 0.00 + 0.13	1.13

All four nights are marked. Change them to 8-hour nights and the scores drop to 1.06, 1.12, 1.23 and 1.42: only the 4th stays over the line.

How to read the result, and its limits

It is a relative score from pooled industrial injury studies. 1.30 means about 30% more injuries and accidents than on the reference shift in those studies, not a measured risk for you.
It follows the paper's additive formula but leaves out breaks, which it cannot know, and gives evening shifts a value between day and night, which the paper's index does not state.
Rest between shifts is not included. Use the rest calculator for quick returns.
Few studies covered more than four shifts in a row. Past the 4th, the calculator continues the trend in a straight line, as the paper does, so long runs are the least certain.

Common questions

Why is 1.30 the line?: It is Capillary's default high-burden line, about 30% more risk than a first 8-hour day shift. A first 12-hour day shift scores 1.28, just under it, and a first 12-hour night 1.34. You can change the line in Analytics.
How is this different from the alertness calculator?: This one scores injury risk from shift features; the shift alertness calculator predicts alertness from sleep and the body clock. They can disagree: a 12-hour night from 19:00 and an 8-hour night from 23:00 reach the same predicted low near 05:45, but this calculator scores them 1.34 and 1.06.
Is anything I enter sent or saved?: No. The calculator runs in your browser and sends nothing.

See your own shifts this way.

Bring in your schedule from any scheduling app with its calendar link. Capillary charts your hours, nights, quick returns and hardest shifts. Only you can see it.

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