An error budget is the amount of downtime or failure an SLO permits over a window. If your SLO is 99.9% over 30 days, the error budget is the remaining 0.1% — about 43 minutes of allowed downtime.
Teams “spend” the budget on risk: deploys, migrations, experiments. When it runs low, a common policy is to freeze risky changes and focus on stability until reliability recovers.
Calculate yours with the error budget calculator.
