What’s the best way to investigate unexpected Azure cost increases?

Start with budgets and anomaly alerts at the subscription level, then create baselines for resources that are especially prone to spikes. Historical data makes the alerts much more useful because you can distinguish normal growth from genuinely unusual spending.

A daily export of billing data to a data lake, followed by a Power BI report, works well for larger environments. Include subscription, resource group, resource, service, tags, daily trends, and comparisons with the previous month. That gives you both a high-level summary and enough detail to track down the source of a change.

Good tagging is essential. Tag resources consistently with the project, team, application, and environment, then use those dimensions when analyzing cost changes. Native anomaly alerts can flag unusual spending, while FinOps dashboards and the Microsoft FinOps Toolkit can provide more flexible reporting across subscriptions.

Some third-party tools combine cost-anomaly detection with snapshots of the Azure environment. Comparing snapshots can reveal that a new resource, resized service, configuration change, or deployment happened around the same time as the cost increase. These tools can be useful when native reports show the amount of the increase but not the operational change that caused it.

A simple operational process helps too: review costs weekly for each project, compare them with an established baseline, and check whether changes are explained by higher usage, more users, or a planned deployment. If the increase is not justified, open a ticket and assign someone to investigate it.