How to calculate attendance percentage — and how many classes you can miss

Many colleges and universities set a minimum attendance — 75% is the most common figure — below which students can be stopped from sitting exams. Knowing exactly where you stand, and how much room you have, takes one formula and a little algebra.

Your attendance percentage

attendance % = classes attended ÷ classes held × 100

Attending 33 of 40 classes is 33 ÷ 40 × 100 = 82.5%. Count only classes that were actually held; a cancelled class is not an absence.

How many classes can I miss?

Suppose you have attended 36 of 40 classes, which is 90%, and the requirement is 75%. If you miss the next s classes, your attendance becomes 36 ÷ (40 + s). It stays at or above 75% as long as:

36 ÷ (40 + s) ≥ 0.75, so 40 + s ≤ 48, so s ≤ 8

You could miss the next 8 classes and still be at exactly 75% (36 out of 48). Miss a ninth and you drop below. The Attendance Calculator works this out for any figures.

A useful rule of thumb: once you are exactly at 75%, you can miss one class for every three you attend and stay there. That is just 75% restated — three out of every four.

How many classes do I need to attend to get back to 75%?

Now suppose you have attended 28 of 40, which is 70%. If you attend the next x classes in a row, your attendance becomes (28 + x) ÷ (40 + x). You need:

(28 + x) ÷ (40 + x) ≥ 0.75, so 28 + x ≥ 30 + 0.75x, so x ≥ 8

Eight consecutive classes bring you to 36 out of 48 — exactly 75%. Notice how much harder recovering is than slipping: being five percentage points short took eight perfect classes to fix.

When it can no longer be reached

There is a limit that catches people out. If you have attended 20 of 40 classes (50%) and only 10 classes remain in the term, the best you can possibly finish on is 30 out of 50 — 60%. No amount of effort reaches 75% in the time left. The calculator checks your target against the classes remaining and tells you plainly when that has happened, so you can speak to your department early instead of discovering it at exam time.

A general formula

For anyone who prefers to work it out by hand, with a requirement written as a decimal r (0.75 for 75%):

• Classes you can miss = attended ÷ r − held, rounded down.
• Classes you must attend = (r × held − attended) ÷ (1 − r), rounded up.

Check with the examples: 36 ÷ 0.75 − 40 = 8 classes to miss, and (0.75 × 40 − 28) ÷ 0.25 = 8 classes to attend.

Rules vary — check yours

• Per subject or overall? Some institutions apply the requirement to each course separately, some to the total. A healthy overall figure can hide one course that is below the line.
• Lectures, labs and tutorials may be counted separately, or labs may count for more.
• Medical and approved absences are sometimes excused or “condoned” up to a limit, usually with documents submitted promptly.
• Late arrivals may count as absences after a certain number of minutes.

Your student handbook or department office is the authority on all of these; the calculator simply uses the figures you enter.

Keep a buffer

The number of classes you can miss is a safety margin for illness and emergencies, not a target. Spending it early leaves nothing for the week you genuinely cannot attend. Checking your figures every few weeks, rather than at the end of term, is the simplest way to avoid an unpleasant surprise. For the marks side of the same term, see how to turn a test score into a percentage and a letter grade.