add up vs tot up

add up and tot up both are verbs.

Word	Noun	Adjective	Verb	Adverb
add up	No	No	Yes	No
tot up	No	No	Yes	No

As verbs, add up and tot up are synonyms defined as:

Other synonyms of add up include add, add together, sum, sum up, summate, tally, tot, total, tote up.

add up (verb)	tot up (verb)
determine the sum of	determine the sum of
be reasonable or logical or comprehensible
to measure up to in kind or quality
add up in number or quantity