I Was Doing Pricing Math on Napkins. So I Built a Cost Estimator.

I run multiple businesses across multiple locations, and for years the "system" for figuring out what a job or an order would cost us was me, doing the same math over and over. On paper, in my head, in a half-broken spreadsheet nobody trusted. What do we need, what does it run us, what's left over for us.

The math itself isn't hard. The problem is you redo it constantly, you redo it slightly differently each time, and every so often you miss something and get an expensive surprise after you've already bought the materials. That last part is what finally pushed me. I got burned on something I should have caught, and I decided the math was going to live in a tool instead of my head.

Step one: I described what I wanted

I opened the AI tool I use and typed roughly this:

"Build me a planner and cost estimator. I want a running materials list tied to real costs. When I plan a job or an order, it should tell me what we need and what it'll run us before we ever buy anything. Flag anything that looks off so I catch the surprises ahead of time instead of after."

Notice that everything in there is business knowledge, not technical knowledge. What we buy, what it costs, how I want to see it. I've never met an owner who couldn't write that paragraph about their own pricing. Most just don't know that paragraph is now enough to get software built.

Step two: I reacted to what came back

The first version showed up fast, and it was decent but not mine yet. So I gave notes, the same way I'd give notes to a sharp employee who took a first crack at something.

• "The materials list needs to be one running list I keep updated, not something I retype per job."
• "Show me the total before I commit to anything, not after."
• "Make the numbers I actually decide with big, and hide the rest unless I ask."

Each round of notes took a few minutes. A few rounds in, it stopped being a generic calculator and became the way I actually price things, just running on a screen instead of in my head.

What it's like now

Now planning starts with the tool. We know what we need and what it'll run us before we ever buy. The expensive surprises get caught while they're still cheap, which is to say before the money leaves. And when my pricing rules change, I don't rebuild anything. I tell the tool the new rule and it's updated.

The napkins are gone. So is the low-grade worry that I forgot something.

Your pricing rules can do this too

Here's the part that matters: there was nothing special about my math. Every owner has pricing rules. A contractor bidding a job, an HVAC company quoting an install, anyone who has ever eaten a cost they should have seen coming. If you can explain how you price to a new hire, you can have those rules turned into a calculator that never forgets a line item and never does the math differently on a tired day.

The tool costs me nothing monthly beyond the roughly $20 a month I already pay for AI. The skill isn't coding. It's describing what you want and reacting to what you get.

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