The question behind the percentage
Working out what percentage of classes you have attended is easy arithmetic. The question students actually have is harder and more useful: given where I am now, how many can I still afford to miss? — or, if you are already short, how many must I attend in a row to climb back? This calculator answers all three at once.
Those last two are not the same calculation as the first, because every class you skip changes both halves of the fraction. Missing one class does not merely fail to add to your attended count; it also raises the total held. That is why attendance falls faster than people expect and recovers more slowly than they hope.
Using this attendance calculator
Enter the classes you have attended, the total held so far, and the attendance you are required to keep — 75% is the most common threshold, which is why it is the default. You get your current percentage, the number of classes you can still miss while staying at or above the requirement, and the number you must attend consecutively to get back to it if you have already slipped.
Only one of the last two will be meaningful at a time: above the line, the number to watch is how many you can miss; below it, how many you must attend. The page also offers a sentence mode if you prefer reading the question as a sentence rather than filling a form.
The formulas, worked through
Your percentage is attended ÷ total × 100. Say you have attended 42 of 60 classes: that is 70%, which is below a 75% requirement.
To find how many you must now attend without missing another, solve for the point where the fraction reaches the target. Attending the next x classes gives (42 + x) ÷ (60 + x), and setting that equal to 0.75 gives x = 12. Twelve classes in a row, with no absences, brings you back to exactly 75%.
Going the other way, if you were at 50 of 60 — 83.3% — the question is how many you can miss before 50 ÷ (60 + x) drops below 0.75. That holds until x = 6, so six more classes could be missed. Notice the asymmetry: climbing back from 5 points below the line took twelve classes, while a cushion of 8 points above it buys only six absences. Recovering is always harder than it looks.
Where the number and the register disagree
A few things worth knowing before you rely on the result. The calculation assumes every class counts equally, which is not always true — many institutions track attendance per subject rather than overall, so an aggregate of 80% can hide a single subject sitting at 60%, and it is usually the per-subject figure that decides eligibility. Run this once per subject if that is your case.
Medical and institutional leave is often exempted, but only once it has been formally approved and entered; until then the register shows an absence. Labs and tutorials sometimes carry separate minimums from lectures. And the totals only cover classes held so far — the classes still to come this term are your real margin, so a figure that looks unrecoverable in week four often is not.
If you want to work with the raw percentages instead — what percent one number is of another, or the change between two — the percentage calculator covers that directly.
FAQ
How is attendance percentage calculated?
Classes attended divided by classes held, times 100.
Count classes, not days, unless your institution tracks whole days. A day with three lectures is three entries.
How many classes can I miss and still keep 75%?
It depends on how many you've already attended, because every class you skip raises the total as well as the misses. The rule is:
With 42 of 60 attended you're at 70% — already below, so the answer is none. With 50 of 60 you're at 83.3%, and you could miss 6 more before dropping to 75%.
The allowance shrinks as the term goes on. Miss classes early and you can make them up; miss them in the last month and you can't.
I'm below the minimum. How many classes do I need to attend?
Enough consecutive classes that the ones you add outweigh the ones you missed:
At 42 of 60 with a 75% requirement, you need the next 12 in a row — that takes you to 54 of 72, which is exactly 75%. Miss one along the way and the count resets higher.
This assumes there are that many classes left in the term. If there aren't, the target is out of reach and it's worth talking to your department early rather than late.
Why is 75% the usual requirement?
It's the most common minimum for exam eligibility, but it isn't a law of nature — some institutions set 60%, some 80%, and some count lab and lecture attendance separately. A few allow medical exemptions that are excluded from the total entirely.
Set the requirement field to whatever your own handbook says. Don't assume 75% because a calculator defaulted to it.
Does the calculator round in my favour?
No, and neither will your institution. Classes you can miss is rounded down and classes you must attend is rounded up, because a fractional class doesn't exist and both roundings have to fall on the safe side of the threshold.
74.6% is not 75%. Many institutions won't round it up for you either, so treat the number this calculator gives you as the hard floor.