AWS billing bug shows some customers billion-dollar cost estimates

Amazon Web Services said Friday that a billing software problem caused Cost Explorer to show inaccurate estimated charges, triggering customer alerts with figures that in some cases reportedly reached billions of dollars. The issue matters because AWS billing thresholds are part of how cloud teams monitor spend and catch misconfigurations, and false alarms at this scale can disrupt finance and engineering workflows even if no actual charges are involved.

AWS posted an issue on its Health Dashboard at 1:33 a.m. Pacific time saying Cost Explorer was “reflecting inaccurate estimated billing data.” The company said it identified the cause within about 90 minutes as “an issue with unit pricing within the estimated billing computation subsystem.” It did not provide a fuller technical explanation.

AWS later paused estimated bill updates. The company said customers might still see inflated numbers already displayed in the billing console, but that those estimates would not continue to rise while updates were paused. AWS said the displayed estimates did not represent actual usage or charges, and said customers did not need to take action.

The company also said a full fix could take multiple hours after mitigation because it would need to recompute estimated billing data. AWS said it was pursuing multiple options, including reverting to the last known good estimated bill computation and rolling back a recent change to the billing computation subsystem. In a later update, AWS said the rollback of the billing computation subsystem change had not resolved the issue.

Users report extreme billing alerts

Customers on Reddit and Hacker News reported receiving automated overage emails for unusually large amounts. Screenshots posted to Reddit showed one user whose AWS charges were listed as $0.19 for the prior month receiving an estimated bill of nearly $2.5 billion.

Other Reddit users claimed they had received estimated monthly charges ranging from $126,000 to $2.5 trillion. Hacker News users also reported estimated bills in the billions. AWS said the numbers appearing in customer accounts were inaccurate estimates, not actual charges.

The incident is a reminder that estimated cloud billing is a software product in its own right, with its own failure modes. Cost Explorer and billing alerts sit between raw usage data, pricing rules and customer budgets. When that layer breaks, customers may see alarming numbers before invoices are finalized, even if the underlying consumption has not changed.

AWS had not disclosed how many customers were affected, which services were involved, whether specific regions were impacted, or whether any customers were at risk of being charged the displayed amounts. The company declined to explain the issue beyond directing inquiries to the Health Dashboard.

For cloud buyers, the practical distinction is between estimated billing data and final invoicing. AWS said the estimates were wrong and that customers did not need to act. The unresolved part is operational: when the billing console will again show accurate estimates, and what recent change caused a core cost-reporting system to produce figures far outside normal bounds.

This story draws on original reporting from The Register.