Is there magic math to decreasing?

I am knitting a hat for my son totally off cuff without a pattern. I was wondering if there is any special math to take into consideration when it comes time to decrease? My current plan is to K2tog, K 5for that row, then knit a row, k2tog, k4, knit a row…etc down to k2tog for the rest of the hat. I cast on 66 stiches, using size 10 1/2 dpns, worsted weight yarn.

66 is a multiple of 11. So to make your decreases come out even you would k9, k2tog around and then decrease in the same manner as you stated.

To figure this out - If you add the 9 + 2 you get 11 and 11 is a multiple of 66. After I figured out what multiple it was I subtracted the 2 for k2tog and I ended up with 9.

Some numbers (62 for instance) don’t work out. Always try to CO a number that works for ease of figuring it out. If you did happen to CO 62 you could throw in a couple decreases or increases to bring it to a number that you can decrease evenly with.

Make sense or did I totally confuse you? It took me a while to figure this out so keep practicing and don’t sweat it. It’s just a hat.