A few years ago a video about "mom math" went around. Cara Nicole (@chaoswithcara on Instagram) explained it: to be somewhere at 9:00 with kids, you work backwards. Shoes by 8:20. Breakfast by 7:15. Which means dressed by. Which means up by. Which means last night.

I watched it and recognized the format. Then I recognized myself, and not in the role I'd have picked.

Dad math

When our daughter was younger, my wife would sometimes ask me to do a drop-off. School, on a day she was sick. Soccer practice on a weekend.

Here's the dad math for a 9:00 practice.

It takes fifteen minutes to drive. Leave at 8:45.

That's it. One variable, one operation. And I am punctual, so at 8:40 I was in the car. At 8:43 I was in the car looking at the clock. At 8:46 I was in the car, stressed, wondering why my daughter wasn't in the car, computing how late we were going to be.

The thing is, dad math isn't wrong. For a problem with one input, it's the right algorithm. If I'm leaving the house alone, "leave at 8:45" is the whole answer.

The problem is that I wasn't leaving the house alone. And the reason my daughter wasn't in the car yet is that the rest of the math was still running inside.

Mom math

Here's what was happening in the house while I watched the clock. I have to reconstruct it, because at the time I didn't know, and that is the point of this post.

Practice at 9:00. So out the door by 8:45, which means my daughter dressed by 8:30, which means the uniform had to be clean, which means it went in the wash some earlier day, which my wife knew because she knew when the last practice was. Shin guards and cleats found, which means they'd been put back somewhere findable after the last time, by someone who wasn't me. Water bottle filled. Snack packed, which means there was a snack in the house and it went on the grocery list earlier in the week. Hair done. Whatever the coach had emailed that week, already read and handled.

That's my best guess at the list. I'm sure it's incomplete, and I'm sure my wife could correct it from memory, because she's the one who was running it. I sat in that car for years and couldn't have named four items on it.

Count the operations. Then count how many of them happened on a different day than the one I was sitting in the car for.

"Leave at 8:45" was the last line of her proof. I'd been reading the last line, calling it the answer, and getting annoyed that the proof was taking so long.

Carry the one

Every one of those steps is a carry. Something from an earlier column that has to be held in your head and brought forward to the next one, or the whole sum is wrong.

In mom math, there are a lot of carries. The snack carries from the grocery run. The clean uniform carries from wash day. The cleats carry from wherever they were put away last Saturday.

And here's the part that took me too long to see: the carrying is the work. Not the driving, not even the packing. The holding of a dozen small things across days so they all land at 8:45 on the right morning. I did the driving. She carried the one. She carried all of them.

I was stressed in the car because I could see the one number I was responsible for. She wasn't stressed in the car because she wasn't in the car. She was still carrying.

Show your work

There's a reason dad math fits on a sticky note and mom math doesn't. Nobody asks dad math to show its work. "Leave at 8:45" sounds complete, so it never gets audited.

Mom math never gets written down either, but for the opposite reason. It's too long, it's running in the background, and the person doing it has been doing it so long she doesn't notice it's math anymore. It just feels like being tired on a Saturday morning for no reason she can name.

I build systems for a living. I spent years making sure the compute that matters gets logged, monitored, and alerted on. The most load-bearing computation in my own house ran with zero observability for two decades.

The only alert was my wife, occasionally, and I treated that as noise.

Order of operations

The fix isn't for me to become a mom-math genius overnight. I'm a dad-math person. Single variable, clean answer, happy.

The fix is to change the order of operations. Instead of her doing all the back-solving and handing me the last line, the back-solving has to happen somewhere I can see it, in pieces I can take.

That's the problem Melo is built around. My wife puts the 9:00 thing into it. It works backwards the way she would, and the carries come out as separate items: the snack, the form, the wash, the gas. Each one has enough detail attached that I can take it without asking her to show her work again. The tasks that need to happen on Tuesday show up on Tuesday, keeping Saturday morning clear.

She still does mom math. She's better at it than any app. But she's no longer the only place the carries live, and I've gone from reading the last line to doing some of the arithmetic.

If you're a dad-math person, here's a word problem. Pick your next 9:00. Before you compute "leave at 8:45," list everything that has to be true for that line to work. Then check how many of those things you had anything to do with.

Show your work. That's the whole post.

Melo is available on iOS and Android.