Excel Formulas You'll Actually Use — Sum, Average & Percent
Last verified: October 2026
Excel has hundreds of formulas; you need about five. SUM, AVERAGE, percentages, copying down, and reading error messages — explained in plain English. Rather have a hand? My number is (330) 200-8042.
The Excel Formulas Worth Knowing, at a Glance
People treat Excel formulas as a dark art, but a household needs only a handful. Every formula starts with an equals sign. =SUM(B2:B10) adds a range; =AVERAGE(B2:B10) finds the typical value; for a percentage you divide (part by whole) and click the % button, or multiply to apply one. Copy a formula down a column with the little fill handle, and read error messages like #DIV/0! and #VALUE! as simple clues. It all works the same in free Google Sheets and LibreOffice Calc. This guide explains each one plainly, and there's a printable 29-page version up top.
Common Questions
1 What formulas do I actually need at home?
Mostly just =SUM (adding) and =AVERAGE (typical value), plus the percentage trick when needed. The AutoSum button even writes the first two for you.
2 How do I write a formula?
Click a cell, type an equals sign, then the calculation — like =SUM(B2:B10) — and press Enter. Point at cells rather than typing numbers so results update themselves.
3 How do I figure a percentage?
To find one, divide the part by the whole (=B5/B20) and click the % button. To apply one, multiply — =B2*1.15 adds 15%, =B2*0.85 takes 15% off.
4 What do error messages like #VALUE! mean?
They're clues to one cell. #VALUE! means text where a number's needed; #DIV/0! means dividing by zero; ##### means the column's too narrow. Each has a quick fix.
5 How do I apply a formula to a whole column?
Write it once, then drag the little square at the cell's bottom-right corner (the fill handle) down the column — or double-click it. Excel adjusts the formula for each row automatically.
6 Do these work without Excel?
Yes — Google Sheets and LibreOffice Calc use the identical formulas. Everything in this guide applies to them too.
Would You Rather I Just Help?
Teaching the handful of formulas that actually help at home is one of my favorite lessons — there's real delight in watching Excel do your sums for you. We'll start with the buttons and ease into typing, as slowly as you like. $99 flat for a visit, or $49 on-screen, 30-day come-back-free.
Would you rather I just do this for you?
No shame in it — plenty of folks would rather hand it off, and that's what I'm here for. I'll come to your home, set it up right, and make sure it's working before I leave. Flat $99 per visit — no jargon, no upsell, and every visit is 30-day come-back-free.
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