Reckon up
Definition 1 of 2
Pro Tip 1/3Mathematical Context
Often used where numbers are involved and a precise total is needed. 
Before we finalize the budget, we need to reckon up all expenses.
Pro Tip 2/3Not Guesswork
Indicates a calculated and deliberate process, not a rough estimate. 
The accountant will reckon up the year-end financials accurately.
Pro Tip 3/3Often Financial
Commonly appears in discussions about money or expenses. 
Let's reckon up the bill and see how much each of us owes.