Accruing LLM spend you have incurred but not been billed for

Accounting wants cost recognised in the period it was incurred, and providers invoice after the period ends. That gap is ordinary and every finance team handles it with an accrual. What makes LLM spend awkward is that the usual accrual basis, last month's actual, assumes the thing is roughly flat, and a growing AI product is the least flat line on the ledger. So the accrual is wrong by roughly the growth rate, every month, in the same direction, and it corrects as a prior-period adjustment that makes the following month look worse than it was. Run that for a few quarters and gross margin is understated during growth and overstated during a slowdown, which is precisely backwards from what anyone reading the numbers needs. The fix isn't a better estimate. It's to stop estimating: if every call was priced when it happened, the month's cost is a sum on the 30th and the invoice becomes a reconciliation rather than a revelation.

• You accrue AI spend from last month's invoice because nothing else is available.
• Every month opens with a prior-period adjustment for the last one.
• Gross margin gets restated after the provider invoice lands.
• Nobody can give finance a cost figure until the invoice arrives.
• Your accrual has been under by a similar percentage several months running.

1. Find the last three months' accruals and the invoices that settled them, and size the gaps.
2. Check whether the gaps run in the same direction, which tells you the cause is bias rather than noise.
3. Ask whether you could produce a cost figure for this month on its last day.
4. Check whether your provider's billing period actually matches your accounting month.

Illustrative example

A modelled service on Claude Haiku 4.5 at real rates of $1.00 and $5.00 per million from the price book effective 2026-07-02. March runs 8,000M input and 900M output tokens. April grows to 11,000M and 1,300M. Finance closes April on the 30th and accrues at March's actual, because that's the only figure it has. Token volumes are modelled.

April closes $5,000 light, which is 28.6% of what it actually cost, and the correction lands in May as somebody else's problem. Nothing here is an estimating failure. The figure existed on the 30th of April, in the call log, unpriced.

The provider knows what it will bill you and tells you on its own schedule, which is a billing question rather than an accounting one, and it may not line up with your close. The only way to have the number on the last day of the month is to have priced each call as it was made, from a rate book that knows what was in effect on that date. Culpa does that in exact decimal, keeps the ledger on infrastructure you control, and carries the same customer, team and feature attribution into the accrual that it carries into margin, so the month closes split the way the business is actually run. The invoice then reconciles against it, and a difference becomes a question about the provider rather than a restatement of your own numbers.

• LLM Cost Anomaly Detection: The Aggregate Has a Noise Floor
• LLM Eval Job Cost: The Line Item Nobody Watches
• LLM Fast Mode Pricing: 2x, Except Where It Runs 2.5x
• LLM Observability Consolidation: Six Tools That Changed Hands