Accruing Usage-Based AI Bills at Month-End

For most brands, software used to be the easiest line in the close. A seat licence costs the same every month, the invoice arrives on time, and the bill is coded to the same account as last month. AI tools are changing that. More of them are billed on usage, and a usage bill behaves less like a subscription and more like an electricity bill: the cost builds up during the month, the amount is not known in advance, and the invoice can arrive after the books for that month are meant to be closed.

What the survey found

Deloitte's third-quarter 2026 CFO Signals survey, published on 21 October 2026, asked 200 CFOs about how they govern AI costs. The authors note that commercial AI providers increasingly charge per token rather than per user seat or at a flat rate, and that bills can spike quickly because of large context windows or long conversation loops.

Two findings stand out for anyone who runs a close. 53% of respondents mainly review AI usage costs after the fact, from vendor bills, periodic reports, dashboards or manual analysis, while 47% monitor them in or close to real time. And if costs go over approved limits, 74% say they would typically pause the related usage within several business days to several weeks, against 19% who would act the same business day.

The caveat matters: the respondents run North American organisations with at least US$1 billion in revenue, so this is not a survey of Australian Shopify brands. But the mechanics are the same at any size. If the only time anyone looks at AI spend is when the invoice arrives, the cost has already been incurred, and in many cases it belongs to a month you have already closed.

Why usage billing breaks a seat-based close

A usage bill causes three problems that a flat subscription does not.

• Timing. The usage happens in October, but the invoice may be issued in November. If you only book the bill, October's expenses are understated and November's are overstated.
• Amount. The figure changes every month, so last month's bill is a poor estimate for this month's.
• Currency. If the provider prices in US dollars, the Australian dollar cost is not known until you choose an exchange rate.

The fix for all three is a month-end accrual, built from the provider's own usage data rather than from a guess.

Step 1: Measure the usage in your period

Most providers publish usage and cost data while the month is still running. As one example, Anthropic's Usage and Cost API reports costs in US dollars, in daily buckets, and says data typically appears within five minutes of a request completing. Other providers offer similar dashboards. Whichever you use, export the cost for the period and keep the export as the support for the accrual.

Watch the time zone. The API's examples use UTC timestamps, and Sydney has been on daylight saving time (UTC+11) since Sunday 4 October 2026. Midnight at the start of 1 November in Sydney is 1:00 pm on 31 October in UTC. A cost report for "October" in UTC days therefore covers roughly 10:00 am on 1 October to 11:00 am on 1 November, Sydney time.

For most brands that offset of ten or eleven hours at each end is immaterial. What matters is picking one cut-off convention, writing it down and using it every month, so that no day's usage is counted in two months or dropped from both.

Step 2: Translate it into Australian dollars

The accounting standard for foreign currency is AASB 121 The Effects of Changes in Foreign Exchange Rates. Three paragraphs do most of the work here:

• Paragraph 21 says a foreign currency transaction is recorded on initial recognition at "the spot exchange rate between the functional currency and the foreign currency at the date of the transaction".
• Paragraph 22 allows a practical approximation: "an average rate for a week or a month might be used for all transactions in each foreign currency occurring during that period", but adds that "if exchange rates fluctuate significantly, the use of the average rate for a period is inappropriate."
• Paragraph 23(a) says that at the end of each reporting period, "foreign currency monetary items shall be translated using the closing rate". An accrued liability to be paid in a fixed or determinable number of US dollars fits the standard's definition of a monetary item.

Paragraph 28 then sends the difference between the rate used at recognition and the closing rate to profit or loss.

Usage builds up day by day, so a monthly average rate for the expense is the natural fit for paragraph 22. The accrued liability then sits at the closing rate on the last day of the month, and the gap between the two is a foreign exchange gain or loss.

A worked example

Suppose the October cost export shows US$1,842.60 of usage, and no invoice has arrived. The rates below are illustrative, quoted as US dollars per Australian dollar:

The Australian dollar weakened over the month, so the same US$1,842.60 costs more to settle at month-end than it did on average during the month. The October journal is:

It balances: $2,813.13 plus $21.64 is $2,834.77. Where rates have barely moved, the exchange line will be small, and you may decide it is immaterial. That is a judgement for you and your accountant, but whatever method you choose should be written down and used every month.

Step 3: Check the invoice when it arrives

In November, reverse the accrual and book the invoice. Before you do, compare them:

1. US dollar amount. Does the invoice agree to the US$1,842.60 you accrued? A difference usually means credits, a different cut-off from the one you used, or charges your export did not include.
2. Australian dollar settlement. If the bill is paid by card, the bank line shows the Australian dollar amount actually charged. The difference from the accrued amount is a realised exchange gain or loss under paragraph 28.
3. GST. Code the bill to the GST the invoice actually shows. Offshore invoices do not always look like Australian tax invoices, so if it is unclear whether GST should have applied, raise it with whoever prepares your BAS rather than guessing.
4. Ownership. Where a provider breaks costs down by workspace or API key, map each to a cost centre or owner, so an unexpected jump has someone to explain it.

What this means for your close

The accrual and the cost control are the same task. Pulling the usage export at month-end gives you a correct expense for the period, and it also puts AI spend in front of a person at least once a month, before the invoice arrives. Pull it mid-month as well and you catch a spike while it can still be stopped, which is the gap the Deloitte figures point to.

A short checklist for each close:

• Export usage and cost for the period from every usage-billed AI provider.
• Apply your documented cut-off and exchange rate method.
• Book the accrual, with the export attached as support.
• In the following month, reverse it and reconcile it to the invoice and the card charge.

The principle is the one we apply to payouts: every number traces back to a source document, and the arithmetic is done by code, not estimated. We set out why in Why Finance Needs Deterministic Agents. If you would like to see that applied to a month of your own Shopify, Stripe, PayPal and Afterpay payouts, you can join the Vert pilot.