Miss one class and you lose a little under one percent. Attend one class and you gain about the same. Most students assume that symmetry, and it is wrong in a way that costs people their exam form.
Sit exactly on 75% with 60 of 80 classes attended, skip one lecture, and you drop to 74.07%. Getting back over the line takes three more classes, not one.
That number doesn't depend on the length of your semester, how many classes you have attended, or how early in the term you are. It depends only on the target percentage, and at 75% it is always three.
Table of contents
- The 1:3 rule
- Where the three comes from
- Recovery cost at other targets
- Banking attendance
- What the 75% rule says on paper
- Bunk budget for a 15 week semester
- FAQ
- Sources
The 1:3 rule
Your attendance is a fraction: classes attended over classes held. When you miss a class, the denominator grows and the numerator stays put, so you take the hit twice. Attending a class grows both, which is why recovery is slow.
I checked whether the three holds across the semester or is an artefact of round numbers. Starting from exactly 75% and missing one class:
| Classes held | Attended | After one bunk | Classes needed to recover |
|---|---|---|---|
| 40 | 30 | 73.17% | 3 |
| 80 | 60 | 74.07% | 3 |
| 120 | 90 | 74.38% | 3 |
| 160 | 120 | 74.53% | 3 |
The percentage you drop to keeps shrinking, and that is what fools people. Late in the term one bunk looks almost free, a 0.47% dent, but the repair bill is the same as in week two.
Where the three comes from
Say you need p percent and you have just missed a class. Attend n more and your record becomes (a + n) / (t + n). Set that equal to your target and a and t cancel, leaving p / (100 - p) as the number of classes you owe per class missed.
At 75 that is 75 / 25, which is 3. Nothing about your own record appears in the answer, so nothing about your record can change it. Memorize it before your next 8am lecture: at a 75% requirement, one bunk is a three class debt.
Recovery cost at other targets
Colleges don't all use 75, and the ratio makes the gaps between requirements much sharper than the percentage points suggest.
| Attendance target | One bunk costs |
|---|---|
| 50% | 1 class |
| 65% | 1.86 classes |
| 66.67% (two-thirds) | 2 classes |
| 75% | 3 classes |
| 80% | 4 classes |
| 85% | 5.67 classes |
| 90% | 9 classes |
Moving from a 75% rule to an 80% rule sounds like a five point tightening, but it raises the cost of every bunk by a third. At 90%, a lab you skip for a wedding takes nine consecutive classes to erase. For a subject that meets three times a week, that is three weeks of perfect attendance to pay off one afternoon.
The formula divides by 100 - p, and at 100 that is zero. Once you have missed a single class, a cumulative 100% is out of reach for the rest of the term, however many you attend afterwards. Our attendance calculator says "not reachable" for that case instead of printing a nonsense figure.
Banking attendance
The same arithmetic works in your favour. Every class you attend above the line banks a fraction of a future bunk, at the same 1:3 rate running backwards.
On an 80 class record at a 75% target:
| Attended | Percentage | Bunks you can still afford |
|---|---|---|
| 60 | 75.00% | 0 |
| 61 | 76.25% | 1 |
| 63 | 78.75% | 4 |
| 66 | 82.50% | 8 |
| 69 | 86.25% | 12 |
| 72 | 90.00% | 16 |
Three extra classes attended in September buy you four free absences later. That is a better reason to turn up in the first two weeks than being told attendance is mandatory. Front-load the term and in November you are spending your own savings instead of begging for a medical certificate. Credit is spendable at that rate, while debt costs three to one.
What the 75% rule says on paper
CBSE sets the requirement at 75% of working days for Class 10 and 12 candidates under Rules 13 and 14 of its Examination Bye-Laws, and reiterated it for the 2026 board exams. It allows relaxation only in defined cases, such as medical emergencies or representing the country in sport, decided on documentation rather than on request.
Higher education is less uniform than the repeated number suggests. Many technical universities and NIT-style regulations use 75% for end-semester eligibility. Delhi University's Ordinance VII sets two-thirds, roughly 66.67%, and lets a student between 40% and two-thirds appear and make up the shortfall in the following semester.
The two rules split the same record differently:
| Record | Percentage | At 75% | At two-thirds |
|---|---|---|---|
| 60/90 | 66.67% | Short | Eligible |
| 64/90 | 71.11% | Short | Eligible |
| 66/90 | 73.33% | Short | Eligible |
| 68/90 | 75.56% | Eligible | Eligible |
Check your own institution's ordinance rather than a number a senior quoted you. You could be comfortable under one rule and debarred under another, a four class difference in this table. Also check whether your college counts per subject or in aggregate. Aggregate is kinder, since a strong subject can carry a weak one. Per subject, one badly timed 8am slot can hold back your whole form, and a percentage calculator is quicker than doing six subjects by hand.
Bunk budget for a 15 week semester
Take a subject with five classes a week over 15 weeks, so 75 classes held. Attend everything and you are at 100%. The cutoff sits here:
| Classes missed | Record | Percentage | Status |
|---|---|---|---|
| 10 | 65/75 | 86.67% | Safe |
| 15 | 60/75 | 80.00% | Safe |
| 18 | 57/75 | 76.00% | Safe |
| 19 | 56/75 | 74.67% | Short by 1 class |
| 20 | 55/75 | 73.33% | Short by 5 classes |
Eighteen absences is more slack than the panic suggests, a little over one a week. The 19th leaves you one class short and the 20th five, because once the term ends there are no classes left to attend and the shortfall is final.
The drop is a cliff, not a slope. You are fine at 18 and short at 19, and by the time the attendance sheet goes up in the last week there is nothing left to fix. Work out your number in week two, not week fourteen.
FAQ
How many classes can I miss to keep 75% attendance?
A quarter of the total held, if you attend everything else. With 75 classes in a semester you can miss 18 and sit at 76%. Missing 19 puts you at 74.67%, short.
Does the recovery cost change later in the semester?
No. The percentage you drop to gets smaller as the total grows, but the classes needed to get back to target stay at three for a 75% rule. Late bunks look cheaper and cost exactly the same.
Is the attendance requirement 75% everywhere in India?
No. CBSE uses 75% of working days for board exam eligibility. Universities vary, and Delhi University's Ordinance VII sets two-thirds with a discretionary provision below that. Check your own institution's ordinance.
Does medical leave count as attendance?
That depends on your institution's rules, and it generally requires documentation submitted through the proper channel rather than an explanation after the fact. CBSE permits relaxation in defined cases such as medical emergencies, decided on evidence.
Sources
- CBSE notice on examination attendance requirements: Rule 13 of the Examination Bye-Laws, Class 10 and 12 eligibility
- CBSE mandates 75% attendance for 2026 board exam eligibility: 2025-26 session reiteration
- CBSE notice on minimum requirements to appear in board examinations: September 2025 clarification
- CBSE attendance rules and exemptions: relaxation categories for medical emergencies and national representation
- University of Delhi Ordinance VII: two-thirds attendance requirement and the 40% discretionary provision
- NIT Kurukshetra revised attendance rules: 75% minimum for end-semester examination eligibility
- Recovery ratios, bunk budgets and the eligibility tables computed for this article from the attendance formula
