Capex vs Opex, Explained: The Accounting Behind the AI Build-Out

Foundations

Capex and opex are the two ways companies spend money, and the accounting difference between them shapes how entire industries are judged. Operating expenditure (opex) is the cost of running the business today: salaries, rent, cloud bills. Capital expenditure (capex) is spending on assets that last: factories, data centres, chips. Opex hits profit immediately; capex is spread over years. That timing difference is currently steering trillions of dollars.

Why the split matters

When a company buys a $10 billion data centre, profit does not fall by $10 billion. The asset lands on the balance sheet and is depreciated: charged against profit over its useful life. So heavy investment suppresses cash flow NOW while barely denting reported earnings, and yesterday’s investment quietly burdens profits for years after. Reading a capex-heavy company means holding both timelines in your head at once.

The AI build-out through this lens

The defining financial story of this era is a capex story: hyperscalers redirecting hundreds of billions from buybacks and margins into chips and data centres. The bull case says today’s capex is tomorrow’s dominant, profitable infrastructure. The bear case asks three accounting questions: how fast should chips be depreciated (shorter lives mean bigger future profit hits); will returns on the assets exceed their cost; and what happens to earnings if the spending must be written down instead of earned back? Every hyperscaler earnings call is, underneath, a debate about these lines.

What to watch in the reports

Capex guidance (the forward commitment), depreciation schedules and any changes to assumed asset lives, the gap between reported profit and free cash flow (capex is the usual wedge), and capitalisation choices: costs booked as assets rather than expenses flatter today at tomorrow’s expense. When commentary says a company’s “earnings quality” changed, this machinery is usually what moved.