ToolsKit

Attendance Shortage Calculator

See your attendance percentage, classes needed to hit a target and classes you can miss.

About this tool

Many colleges and schools require a minimum attendance, often 75%, to sit exams. If you have fallen short, the question is simple but the arithmetic is not obvious: attending more classes also increases the total, so the gap closes more slowly than you expect.

Enter the total classes held so far, the classes you attended and your target. The calculator tells you your current percentage, how many classes in a row you must attend to reach the target, or how many you can still skip if you are already above it.

How to use the Attendance Shortage Calculator

  1. Enter the total number of classes conducted so far (not the whole semester).
  2. Enter how many of those you attended.
  3. Set your target percentage. 75 is pre-filled because it is a common requirement.
  4. Press Calculate and read the result and the step-by-step working below it.
  5. If you are below target, plan to attend that many consecutive classes without absences.

Practical examples

Short of target: 40 classes held, 26 attended (65%). Target 75%. x = ceil((75 x 40 - 100 x 26) / (100 - 75)) = ceil(400 / 25) = 16. After 16 more classes you have 42 / 56 = 75%.
Above target: 60 held, 54 attended (90%). With a 75% target you can miss floor((100 x 54 - 75 x 60) / 75) = 12 more classes.

How it works

Attendance % = attended / total x 100.

Classes needed (attending all of them): the smallest whole x with (attended + x) / (total + x) >= target/100, which rearranges to x = ceil((target x total - 100 x attended) / (100 - target)).

Classes you can miss: the largest whole y with attended / (total + y) >= target/100, which gives y = floor((100 x attended - target x total) / target). A target of 100% cannot be recovered once a class is missed, and the tool tells you so.

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Frequently asked questions

Does the calculator include future classes?

It assumes you attend every upcoming class when computing "classes needed", and miss only the ones counted in "classes you can miss". Plan with your actual timetable in mind.

Why does it give whole numbers?

You cannot attend part of a class, so results are rounded up (classes needed) or down (classes you can miss) to stay on the safe side.

My institution rounds 74.5% up to 75%. Does this tool?

No. It uses the exact value. Check your institution's rules on rounding, medical leave and condonation.

Can I use it for work shifts or training sessions?

Yes. Any "present out of total" situation works the same way.

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Results are for general information. Check important figures against official sources. Read the disclaimer.