Calculator of Alexandria

Final exam grade calculator

Work out the score you need on your final exam to reach a target course grade, from your current grade and the final's weight.

Score needed on the final
Course grade if you score 0
Course grade if you score 100

Formula

x=G−(1−w) gwx = \frac{G - (1 - w)\,g}{w}
How it's derived

The formula

x=G−(1−w) gwx = \frac{G - (1 - w)\,g}{w}

xx is the score you need on the final, GG the course grade you want, gg your current grade and ww the final’s weight as a decimal (25% is 0.25).

Where it comes from

A course grade with a final exam is a weighted average. Your work so far counts for 1−w1 - w of the grade, and the final counts for ww:

G=(1−w) g+w xG = (1 - w)\,g + w\,x

Solving for the unknown exam score xx: subtract (1−w)g(1-w)g from both sides, then divide by ww.

Worked example

Your current grade is 84%, the final is worth 25%, and you want an 85%:

x=85−0.75×840.25=85−630.25=88%x = \frac{85 - 0.75 \times 84}{0.25} = \frac{85 - 63}{0.25} = 88\%

The bounds help too. Scoring 0 on the final would leave you at 63%. Scoring 100 would get you 88%.

Watch out for

  • Over 100% means out of reach. If you need more than 100%, that target isn’t possible through the exam alone.
  • Check how your course weights things. If the final replaces your lowest test, or if categories are weighted separately, this simple average doesn’t apply.
  • “Current grade” should already be weighted. Use the figure from your course portal, not an average of raw scores.

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