Ever wonder if you could predict, with any accuracy at all, when you’ll hit diminishing returns on an advertising buy? It’s pretty important, yet almost impossible to figure out, or so you’d think.

It’s not actually all that hard, if you follow the square root rule. I’m not even going to try to explain it here though. Kevin Hillstrom has a far better explanation of the Square Root Rule than I ever will.

The important thing to note is that yes, all numbers can lie. If your marketing is totally ineffective, or if you lack baseline, historical data, chances are this formula won’t do you as much good.

Here it is again: The Square Root Rule, as explained by a Math Guy