GPU Payback Period: The Naive Math Is Wrong by Over a Year

“¥3.2M server, ¥1.02M annual rent — payback in 3.1 years.” This is the calculation most people do, and it is wrong, because payback is about cumulative net cash flow, not cumulative revenue. Rack fees, maintenance, taxes and financing costs all come out before cash is truly recovered.

The base-case cash curve

In our model (single unit, ¥3.2M total investment, ¥85k/month rent, 90% finance lease), net cash flow in year 1 is about ¥699k and rises slowly. Cumulative net cash flow only turns positive during year 5 — a static payback of ≈4.46 years. And because 20% of total principal is repaid in each of the first 5 years, cash left after principal repayment is thin early on; most recovery happens from year 6 onward.

What moves payback most

• Rent level: −10% rent pushes payback to ≈5.07 years; −20% to ≈6.23 years; −30% means no payback within 8 years.
• Purchase price: at the same rent, every 10% off the purchase price pulls payback forward by roughly half a year or more.
• Financing ratio changes equity returns, not the project-level payback — do not mix the two views.
• Rent decay in years 6–8 mostly affects total profit, not the payback date itself.

Payback is only one lens. The years after payback are where most of the profit sits, so judge a project on payback, IRR and cumulative cash flow together — the calculator shows all three, live.