What SUM does
SUM is the standard addition function in Excel. It can total individual numbers, single cells, multiple ranges, or combinations of all three.
Because it is simple and flexible, SUM appears everywhere from quick totals to large financial models.
Practical examples
Add a continuous range
=SUM(B2:B12)
This is the most common use of SUM and is ideal for column totals.
Add separate values and ranges together
=SUM(B2:B10,D2:D10,F2)
SUM can combine non-adjacent inputs cleanly without using multiple plus signs.
Common mistakes and notes
Numbers stored as text
If values look like numbers but are stored as text, SUM may ignore them. Check alignment, formatting, and data import steps when totals seem low.
Double-counting
Be careful when mixing overlapping ranges, such as B2:B10 and B5:B8. Excel adds everything you give it, including duplicates.
SUM is often better than manual addition
=B2+B3+B4+B5 works, but =SUM(B2:B5) is easier to audit and easier to expand later.