Your biggest customer is probably costing you money.

Not always.

But often enough, it’s worth 10 minutes of your Monday to find out.

Revenue by customer sits at the top of every report where everyone can see it. Cost to serve scatters across service hours, spare parts, night support, delivery, and a discount someone approved two years ago.

So the account looks like your best one.

Because the only number anyone checks says it is.

Every CFO I talk to knows this.

The CEO asks which customers actually make money.

You pull four exports, open a spreadsheet with 14 tabs, split team time on a guess, spread rent by revenue, and walk into the board meeting with a table you’re not confident showing.

Your head of sales tells you not to touch the pricing on the biggest account. You can’t prove him wrong. You don’t fully trust your numbers either.

So I gave the job to Claude instead.

I hand it four exports and two contracts.

And just 10 minutes later a customer P&L comes back, and every number opens to show how it got built.

The 14 tabs are gone, and so is the guess you spend the meeting defending. You click a number, the calculation opens, and the records behind it sit one tab away.

So the analysis stops eating your week, and the decision gets it instead.

In today’s letter, you’ll build:

• A customer P&L in about 10 minutes from four exports and two contracts.

• Every figure clicks down to its calculation, its rules, and its source records.

• Which customer looks best on revenue and sits below break-even.

• Paid subscribers get the skill, the exact prompt, and the test files.

Let’s dive in.

How to build a customer P&L with Claude in 10 minutes

Nothing here waits on IT. No procurement, no ERP upgrade, no pilot committee. You need a Claude account, one skill file, and the exports you already pull every month.

That is what most CFOs miss.

They park AI in next year’s column while the capability sits one upload away, and every month they wait, they keep making decisions on numbers they do not trust.

The demo company is Born2Cycle, our sample business.

It sells bike fleets to hotels and services some of them. Every number is fictional. Run it once on this data, then point the same skill at your ledger.

Step 1: Install the Claude skill

Download the Claude P&L Skill and test files below

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