Pay attention to context; 'add up to' involves accumulation of things, usually numerical. Her weekly earnings add up to her monthly budget.
Pro Tip 2/3
Small Contributions
Understand that 'add up to' can describe how small amounts or acts contribute to a larger whole. A number of small donations added up to a substantial charity fund.
Pro Tip 3/3
Result Emphasis
It emphasizes the result of adding multiple things together. Their joint efforts added up to the project's success.