From Longman Dictionary of Contemporary Englishdo your sumsdo your sumsBritish English informalCOUNT/CALCULATE to calculate whether you have enough money to do something Do your sums first before you decide how much to spend. → sum
Examples from the Corpus
do your sums• We can accumulate the figures and we can all do our sums.• I did my sums and I knew I could pay him.• You will have to do your sums. 