Attendance Percentage Calculator

The formula, and the two that follow from it

The first one is the one everybody knows:

Attendance % = classes attended ÷ classes held × 100

Attended 30 of 40, you are at 75%. The trap is the denominator: it is the classes that have actually been held, not the number scheduled for the whole term. Dividing by the term total in week four makes a perfect record look like 30%.

The other two questions are the ones people actually came for, and both fall straight out of the first.

How many more can I miss?

You want the largest number of further classes n such that, after missing all of them, you are still at or above the target t:

attended ÷ (held + n) ≥ t   →   n ≤ attended ÷ t − held

Then round down, because you cannot miss two-thirds of a lecture, and rounding up here is how a calculator cheerfully tells someone they are fine at 74.6%.

Worked example. 60 attended, 70 held, 75% required. 60 ÷ 0.75 = 80, minus 70 = 10. Miss all ten and you are at 60 of 80 — exactly 75%. Miss an eleventh and you are at 60 of 81, which is 74.07%.

How many must I attend in a row?

This is the question for anyone already short, and it is where intuition fails. You want the smallest n such that attending the next n classes gets you back to the target:

(attended + n) ÷ (held + n) ≥ t   →   n ≥ (t × held − attended) ÷ (1 − t)

Round up this time — a partial class does not save you.

Worked example. 68 attended, 100 held, 75% required. (75 − 68) ÷ 0.25 = 28 classes without a single absence, which takes you to 96 of 128 = 75%. Seven percentage points behind, and it costs twenty-eight classes.

Why a shortfall is so expensive to fix

Look at the two divisors. Missing a class adds one to the denominator only. Attending one adds to the numerator and the denominator, so it only moves you (1 − t) of a class closer — a quarter of a class at a 75% target, a fifth at 80%.

The clearest illustration is the smallest one. Sitting at exactly 75 of 100:

• Miss one class → 75 of 101 = 74.26%
• Attend three in a row → 78 of 104 = 75% again

One absence, three classes to repair. At an 80% threshold the same single absence takes four. This is the arithmetic behind the familiar advice to bank attendance early rather than plan to catch up later: early absences are cheap because the denominator is small, and they get more expensive as the term goes on.

Thinking in absences rather than percentages

If you know the total number of classes the course will hold, stop thinking in percentages entirely and think in absences. A 75% requirement means you may miss a quarter of them, full stop:

That is a budget, and it is far easier to reason about than a moving percentage. Enter the course total in the optional field above and the calculator works out how much of yours you have already spent — and says so plainly if the target has become unreachable, instead of showing a comforting number that cannot actually happen.

What this calculator does not know

Everything above is arithmetic. Everything below is policy, and policy lives in your institution's regulations rather than in any calculator.

• Whether 74.5% rounds to 75%. Some institutions round to the nearest whole number, some floor without exception, and many never write it down. The figure on this page is exact and unrounded so you can see exactly where you sit.
• How medical and approved leave is treated. Some remove the class from the denominator entirely; others add it to your attended count. Both help, by different amounts, and they give different final percentages.
• Whether all classes count equally. A three-hour lab against a one-hour lecture is a weighting question. If your course weights components, run each one separately.
• What the threshold actually is. 75% is common and it is not universal; 60%, 66.67%, 80% and 85% all appear in real regulations, sometimes varying between papers on the same degree.
• What happens if you fall short. Being barred from the exam, a condonation process with its own deadline, a fee, repeating the paper — these vary, and the deadline is usually the part worth finding out early.

Checking the calculator against your portal

If this page and your student portal disagree, one of three things is usually the reason, and all three are worth knowing:

1. Different denominators. Your portal may be counting scheduled classes rather than held ones, or excluding cancelled sessions that you counted.
2. Rounding. A portal showing a whole number is hiding up to half a point either way.
3. Weighting. The portal may be blending lectures and labs with weights you have not applied.

The portal is the record that counts. This page is for working out what to do about it.

Three situations, worked through

Comfortably ahead, wondering about a trip

60 attended of 70 held, 75% required. You are at 85.71%, and 60 ÷ 0.75 − 70 = 10, so you can miss ten more classes and still be exactly on the line at 60 of 80. A week away costing five classes takes you to 60 of 75 — 80% — with five of the ten still in hand.

The thing to check before booking is the course total, not the percentage. If only fifteen classes remain and you miss five of them, the arithmetic above still holds, but you have spent a third of your remaining margin on one trip.

Just under, and worried

68 attended of 100 held. You are at 68%, seven percentage points short. (75 − 68) ÷ 0.25 = 28 classes without a single absence, which takes you to 96 of 128 = 75%.

Twenty-eight is a lot of classes, and whether it is possible depends entirely on how many remain. Enter the course total in the optional field: if fewer than 28 are left, the calculator will tell you plainly that the target can no longer be reached, which is more useful than a number that implies it can.

Exactly on the line

75 of 100, and one class tomorrow. Attend it and you are at 76 of 101 = 75.25%. Miss it and you are at 75 of 101 = 74.26%, and it then takes three consecutive attendances to get back to 75% exactly — 78 of 104.

This is the position where the asymmetry bites hardest, and it is also the position where institutional rounding matters most. At 74.26% you are below the line on any reading; at 74.5% you may or may not be, depending on a rule nobody has told you.

If you are going to fall short

The calculator can tell you that the target is unreachable. What happens next is not arithmetic, and it is worth acting on early rather than at the end of term.

• Find the actual regulation. Not the rumour. The threshold, the rounding rule and the consequence are written down somewhere, usually in a handbook or an academic regulations document.
• Find out whether a condonation process exists. Many institutions have one for medical or compassionate grounds. Almost all of them have a deadline, and it is usually well before the exam.
• Get documentation while it is gettable. A medical certificate is far easier to obtain in the week you were ill than three months later.
• Talk to the person who keeps the register. Marking errors happen, and a class you attended but were not marked for is the easiest kind of shortfall to fix.

Frequently asked questions