What is the Bunk Calculator?
The Classes You Can Skip Calculator — popularly called a "bunk calculator" — tells you exactly how many lectures you can miss while still meeting your institution's minimum attendance requirement (commonly 75%). Many colleges bar students from exams if attendance falls below a set percentage, so knowing your buffer helps you plan days off without risking a detention or shortage.
How to use it
Enter three numbers: the classes you have attended so far, the total classes held to date, and your required attendance percentage. The calculator returns how many future classes you can skip while staying at or above the threshold, plus your current attendance percentage. If you're already short, it shows how many classes you must attend in a row to recover.
The formula explained
If you skip a class, your total still goes up by one but your attended count does not. To stay above the required fraction \(p\) you need \(\text{attended} \geq p \times \text{total}\). Solving for the number of skips you can afford from now gives:
$$\text{Skippable} = \left\lfloor \frac{A - p \cdot T}{p} \right\rfloor \qquad p = \frac{R}{100}$$
where \(A\) is classes attended, \(T\) is total classes held, and \(R\) is the required percentage. The floor rounds down because you can only skip whole classes. If the result is negative you are already below the requirement, and the recovery formula below tells you how many classes to attend instead: $$N = \left\lceil \frac{p \cdot T - A}{1 - p} \right\rceil.$$
Worked example
Suppose you've attended 45 of 50 classes and need 75% (\(p = 0.75\)). Then $$A - p \cdot T = 45 - 0.75 \times 50 = 45 - 37.5 = 7.5.$$ Dividing by \(p\): $$7.5 / 0.75 = 10.$$ So \(\lfloor 10 \rfloor = 10\). You can skip up to 10 more classes and still hold exactly 75% (45 of 60). Your current attendance is \(45/50 = 90\%\).
How to calculate skippable classes by hand
Let \(A\) be classes attended, \(T\) be total classes held, and \(R\) be the required percentage.
- Convert the required percentage to a fraction. Divide by 100: \(p = R/100\). For a 75% rule, \(p = 0.75\).
- Find the minimum attendance the rule demands so far. Multiply \(p\) by the total: \(p \cdot T\). For \(A = 45,\ T = 50,\ p = 0.75\): \(0.75 \times 50 = 37.5\).
- Subtract that from your attended count. This is your surplus above the bare minimum: \(A - p\cdot T = 45 - 37.5 = 7.5\).
- Divide the surplus by \(p\) and take the floor. Each future skip adds 1 to the total but 0 to attended, so each skip costs \(p\) of surplus: \(7.5 / 0.75 = 10\), and \(\lfloor 10 \rfloor = 10\).
Check: skipping all 10 gives 45 attended out of \(50 + 10 = 60\) total, which is \(45/60 = 75.0\%\) — exactly on the line.
FAQ
What if the result is negative? A negative value means you're already below the requirement, so you can't skip any — the tool then shows how many classes you must attend consecutively to recover.
Does skipping add to total classes? Yes — this model assumes every class is conducted whether you attend or not, which is the standard college rule.
Is 75% always the cutoff? No, you set the percentage yourself; many universities use 75%, but some use 80% or 85%.
