1.
see add 2
2.
If facts or events do not add up , they make you confused about a situation because they do not seem to be consistent. If something that someone has said or done adds up , it is reasonable and sensible.
Police said they arrested Olivia because her statements did not add up...
PHRASAL VERB : usu with neg , V P
3.
If small amounts of something add up , they gradually increase.
Even small savings can add up...
PHRASAL VERB : V P