Throughout this series we have followed the money earned by AI providers. Now open the books on the other side of the transaction. When an accounting firm updates a page, the invoice shows its AI subscription. It says nothing about the accountant reading the finished page on a phone.

Compare a finished, publishable page in both cases

Suppose it previously took 60 minutes to update the page yourself. With AI you spend ten minutes preparing instructions, 15 reviewing the first version and ten asking for a correction and checking the live result: 35 minutes of your time. These are illustrative assumptions, not measured figures for our office or a price quote for a particular product.

Value staff time at ¥6,000 per hour and assume a ¥3,000 monthly subscription supports ten similar jobs. An equal allocation gives the following cost per page.

• Previous method: 60 minutes × ¥100 = ¥6,000.
• With AI: 35 minutes × ¥100 + ¥3,000 / 10 = ¥3,800.
• Difference: ¥2,200 per page and 25 minutes of staff time released.

The hourly figure represents an assigned value of time. Using the rate charged to clients implicitly assumes that the released 25 minutes can be sold to another client. Choose the purpose of the exercise first: measuring payroll costs and valuing the owner's scarce time are different questions.

How much extra rework would erase the saving?

Another ten-minute revision reduces the ¥2,200 advantage to ¥1,200. A total of 22 extra minutes brings the two costs level. A first answer can arrive in seconds; the calculation turns on how much staff time it takes to deliver something the reader can actually use.

Volume also matters. If the one page bears the entire ¥3,000 subscription, the AI-assisted cost is ¥6,500, or ¥500 more than before. If the subscription is already paid for another purpose and this page triggers no new charge, its incremental subscription cost is zero. At renewal, the question changes again: compare the full fee with the value of the time recovered over the month.

Record active work separately from waiting

When our website changes I check it on my phone. An unreadable label means real rework. If I can serve a different client while the system processes the request, those minutes do not all belong in the labour cost of this job. Keep elapsed waiting time in a separate column when it matters for delivery.

For one job, record time spent on instructions, time spent inspecting the output, time spent on corrections and rechecking, and additional cash charges. When comparing that with outsourcing, include the time you previously spent briefing and checking the contractor. Compare both at the same quality and delivery stage.

The larger saving may come from solving a recurring design problem once, so that next month the accountant does not have to discover and correct it all over again.