How to calculate student attendance
The attendance percentage formula is simple. The awkward part is keeping the numbers accurate across a whole year – and answering follow-up questions like “how many sessions does she need to reach 85%?”. Here is how to do both.
The basic formula
Attendance percentage = (sessions attended ÷ total sessions) × 100.
Count only sessions that were actually held – if a session was cancelled or the student was not timetabled, leave it out of both numbers, otherwise the percentage is unfairly dragged down.
Worked examples
Example 1: a straightforward percentage
A student attended 30 of 40 sessions. 30 ÷ 40 = 0.75, times 100 = 75% attendance.
Example 2: AM/PM registers
If you mark AM and PM separately, each half-day is one session. Ten teaching days is 20 sessions. A student present for 17 of them has 17 ÷ 20 × 100 = 85% attendance. Decide whether you report per session or per day, then be consistent – mixing the two makes percentages meaningless.
Example 3: sessions needed to reach a target
A student is on 30 out of 40 (75%) and the target is 85%. Assuming they attend every session from now on, the number of consecutive sessions n needed satisfies (30 + n) ÷ (40 + n) ≥ 0.85. Solving gives n ≥ 27 – so 27 consecutive attended sessions to reach 85%. Targets take a long time to recover; that is why early intervention matters more than end-of-year chasing.
Common mistakes
The three errors that most distort attendance figures: counting cancelled sessions in the total; treating an unexplained absence and an authorised absence identically without noting which is which; and calculating percentages over different date ranges for different students, which makes comparisons meaningless.
If you want a quick check, use our free attendance percentage calculator – it does the target calculation for you.
Let the register do the maths
My Register calculates attendance automatically from the marks you take: per student, per class, with punctuality separated and absence patterns flagged. When a college or parent asks for a figure, it is already worked out – and shareable as a live report. It is completely free.