To find the grade you need on the final exam, use this formula:
required = (target - current x (1 - w)) / w
Here target is the overall grade you want, current is your grade going into the final, and w is the final’s weight written as a decimal (30% becomes 0.30). The final grade calculator runs this for you, but the formula is short enough to do by hand once you see how the pieces fit.
What each part means
Your overall grade is a weighted average of two things: the work already graded and the final exam. The final counts for w of the grade, so everything else counts for 1 - w. The formula rearranges that average to solve for the one number you do not have yet, the score you need on the final.
- current is where you stand before the final, as a percentage.
- target is the overall grade you are aiming for.
- w is the final’s weight as a decimal, so a final worth 30% is
w = 0.30.
A worked example that does not work out
Say your current grade is 85%, you want to finish at 90%, and the final is worth 30%.
Put the numbers in:
required = (90 - 85 x (1 - 0.30)) / 0.30
required = (90 - 85 x 0.70) / 0.30
required = (90 - 59.5) / 0.30
required = 30.5 / 0.30
required = 101.7%
The answer is above 100%, which no exam allows. That means a 90% overall is out of reach with this final alone. Even a perfect 100% on the final would not pull your average up to 90%, because the 85% already on the books holds it down. When the calculator returns a number over 100%, read it as “not possible with this exam,” and look at extra credit or a target you can actually reach.
A second example that does work out
Now keep the current grade at 85% and the final weight at 30%, but lower the target to 87%.
required = (87 - 85 x 0.70) / 0.30
required = (87 - 59.5) / 0.30
required = 27.5 / 0.30
required = 91.7%
A 91.7% on the final gets you to an 87% overall. That is a real number you can study toward. The only change from the first example was the target, which shows how much the goal you pick decides whether the result is reachable.
When the target is already secured
Sometimes the formula returns zero or a negative number. That is not an error. It means you have already done enough.
Say your current grade is 95%, you want at least 90% overall, and the final is worth 20%.
required = (90 - 95 x 0.80) / 0.20
required = (90 - 76) / 0.20
required = 14 / 0.20
required = 70%
That one is reachable. But push the target down to 80% with the same numbers:
required = (80 - 95 x 0.80) / 0.20
required = (80 - 76) / 0.20
required = 4 / 0.20
required = 20%
Drop it to 76% and the result hits 0%, meaning even a zero on the final keeps you at the target. Anything below that gives a negative number, which still means the same thing: the target is locked in no matter how the final goes. The calculator reports this as already met so you are not left puzzling over a negative score.
Why the weight changes everything
The final’s weight is the divisor, so it controls how hard the required score swings. A final worth 10% (w = 0.10) divides the gap by a small number, which sends the required score up fast, and small targets can quickly become impossible. A final worth 40% (w = 0.40) spreads the same gap across more of the grade, so the score you need to hit a given target comes out lower. This is why two students with the same current grade and the same target can need very different finals: their finals carry different weight.
Run your own numbers
The formula is the same every time, only the inputs change. Enter your current grade, your target, and the final’s weight into the final grade calculator and it returns the score you need, flags anything over 100% as not possible, and tells you when the target is already secured. To plan further ahead, see how to calculate your GPA and the difference between weighted and unweighted GPA.