SUM and the Basic Math You'll Use Daily
Okay. We've made copies, we've got our tabs, we're not lost anymore. Time to actually make this thing do something.
Sooo here's my real opinion, and I'll die on this hill: you don't need most of the fancy functions people talk about. Ninety percent of running a small business on a spreadsheet is SUM, one lookup formula, and knowing roughly what your numbers should be before the spreadsheet tells you. That's it. If somebody's trying to push you toward something complicated you don't understand yet, just, don't. You'll break it in three months and have no idea why.
So let's start with the one you'll use constantly.
SUM: adding a column without doing it in your head
Click into an empty cell below a column of numbers. Type:
`` =SUM( ``
Then either type the range, like A2:A15, or just click the first number and drag down to the last one. Close the parenthesis. Hit enter.
That's the whole thing. Google Sheets adds up everything in that range and drops the total right there. No calculator, no napkin math, no "I think it's around four hundred."
A couple things that trip people up:
The range has to actually cover your numbers. If you add a new row of sales next week and it's below your SUM range, it won't get counted. Sheets doesn't automatically know to stretch. You either build your range a little longer than you need right now, or you get comfortable clicking in and adjusting it later. I usually build in extra blank rows on purpose, just for this.
Blank cells are fine, text cells are not. SUM will politely ignore an empty cell. But if there's a stray word in there, like you typed "n/a" instead of leaving it blank, Sheets either throws an error or just skips it silently, which is worse because you won't notice.
AVERAGE, COUNT, and the other two you'll actually reach for
You don't need a big list of functions memorized. Just these:
=AVERAGE(range)— tells you the typical value. Handy for "what's my average sale" or "how many hours do I usually spend on a job."=COUNT(range)— tells you how many cells have numbers in them. Good for "how many orders came in this month."=MAX(range)and=MIN(range)— your biggest and smallest number in a range. I use this to catch weird outliers, like if MAX suddenly shows a number that's way bigger than anything else, something got typed wrong.
Same rules apply to all of them. Type the equals sign, type the function name, select your range, close the parenthesis, enter.
Basic math without a formula name at all
You don't always need SUM. Sometimes you just want two cells to talk to each other. Click a cell, type an equals sign, then reference other cells directly:
`` =A2+A3 =A2-A3 =A2*A3 =A2/A3 ``
This is how you'd do something like "price times quantity" for an invoice line, or "total minus expenses" for a rough profit number. Simple, but it's the backbone of basically every business sheet you'll ever build.
Now, check it against reality
Here's the part people skip and shouldn't. Once you've got a total, go check it against something real. Count the actual boxes on the shelf. Look at the actual bank balance. Add up three rows by hand and see if it matches what the formula gave you.
I say this because a spreadsheet will give you a very confident, very wrong answer if your range is off by one row, or if you accidentally typed a number into the wrong column. It won't apologize. It'll just sit there looking correct. You have to be the one who catches it.
I started doing this after I helped my friend Sharlene set up a sheet to track her freezer meal business. Nothing fancy, just orders, cost of ingredients, and what she sold each batch for, with a SUM formula pulling her monthly total. First month she ran it, she texted me a screenshot of her profit number with about three heart emojis. I literally teared up a little standing in the Macey's parking lot reading it. But the reason that number meant something is she'd already been checking it against her receipts the whole month. The formula didn't do the trusting part. She did.
That's really the whole lesson. SUM does the adding. You still have to know, roughly, if the number it gives you makes sense.
Before next time
Go build one SUM formula on something real in your life, even if it's just adding up your grocery receipts from the last two weeks. Then check it against the actual total on the receipt. If it matches, great, you're set. If it doesn't, that's normal too, we'll talk through what usually causes it.