How IB Grades Are Calculated: A Full Breakdown
Jamal Lewis
How IB Grades Are Calculated
"How are IB grades calculated?" sounds like it should have a simple answer, and at the top level it does: six subjects out of 7 points, plus up to 3 bonus points, for a maximum of 45. But that summary hides the part that actually matters to a student trying to improve and how the marks inside each subject get weighted, and how those raw marks get turned into a grade in the first place.
This is the deep-dive version of the explanation on our IB Grades & Scoring pillar page, with a worked example so you can see exactly how a real subject grade gets built.
The Two Layers of an IB Grade:
Every IB grade is really two calculations stacked on top of each other:
- Layer 1 Raw marks: Your Internal Assessment and external exam papers are marked individually then combined into a single total mark out of that subject's maximum. This varies slightly by subject and by SL/HL.
- Layer 2 Grade conversion: That total mark is converted into a 1 to 7 grade using grade boundaries set for that specific subject and exam session, not a fixed percentage scale.
Almost all of the confusion around IB grading comes from treating these as one step instead of two.
Worked Example: Building a Subject Grade:
Here's a simplified example for IB Biology SL, showing how the pieces combine into a total mark before any grade boundary is even applied:
That total mark 18 + 22 + 34 = 74, out of a maximum of 104 in this simplified example is then checked against that session's Biology SL grade boundaries to determine the final 1 to 7 grade, which is why two students with the same raw total in different exam sessions can end up with different final grades.
How the TOK and Extended Essay Bonus Points Work:
Beyond your six subjects, Theory of Knowledge (TOK) and the Extended Essay (EE) are each graded A to E, and those two letter grades are combined using a fixed matrix to produce 0 to 3 bonus points:
A grade of E in either TOK or the EE results in the Diploma being withheld regardless of your subject scores and one of the few genuine "automatic fail" conditions in the whole IB grading system.
Why the Same Percentage Can Mean Different Grades:
Because grade boundaries are recalculated every session based on how the global cohort performed and how difficult that year's paper was, there's no universal "70% = grade 6" rule. A harder-than-usual paper typically comes with lower boundaries to compensate, and an easier paper with higher ones. This is also why practicing against last year's boundaries can be misleading and the boundaries a student sees in November won't necessarily match the ones from the following May.
The only reliable way to gauge where you'd land is to sit a full paper under real conditions and check the result against boundaries from a matching, recent session which is exactly what a properly built mock exam is for.
Put This into Practice:
A free Baccalytics mock exam applies realistic grade boundaries to your result, so you get an honest 1 to 7 estimate, not just a raw percentage that doesn't map to anything.