What grade do I need?
Enter your current average, how many exams you've taken and your target average: get the grade needed on the next exam.
How it works
To raise your average the new grade must «pull up» the set. The formula considers the desired average over all exams, including the next one.
Note
If the needed grade is above the maximum, the goal can't be reached with a single extra exam.
Where the sum comes from
The average you want applies to all the exams, the new one included. So: target average × (exams taken + 1) gives the total of marks needed; subtracting what you've already accumulated (current average × exams taken) leaves the mark for the next exam. In one line: mark = target × (n+1) − average × n. It's the same sum you do to work out what the last month has to bring in to reach an annual total.
Why the more exams you have, the less the average moves
This is the effect that surprises people trying halfway through: after twenty exams, a top mark on the twenty-first raises the average by (top − average) ÷ 21, a few tenths. With an average of 25, a 30 takes it to 25.24. It isn't bad luck, it's arithmetic: every new mark weighs one twenty-first of the total.
Hence the practical consequence worth knowing before chasing a target: raising the average by a full point after twenty exams takes about twenty points spread over the following ones, that is four exams five points above the current average, or ten exams two points above. Early in the record, on the other hand, every single mark moves things a lot, and that's where it pays to play well.
When the number that comes out is impossible
If the mark needed exceeds the top of the scale, the target can't be reached with one exam, and the page says so rather than showing a meaningless number. The right question at that point is a different one: how many exams are needed, and with what marks. You work it out by trying: with two top marks, with three, until the number becomes possible.
Nearby tools
For the average that takes credits into account there is Weighted average, to convert a mark to another scale Grade converter and for the simple average of a list Sum a list of numbers.