agent set the budget alert on forecasted spend, the 100% alert fired on the 3rd of the month

TL;DR

A 100% threshold on forecasted spend will always fire early in the month, because the forecast projects the full month. Put the 100% alert on actual spend, and use forecasted spend only for an early-warning budget at a lower threshold like 80%.

agent set the budget alert on forecasted spend, the 100% alert fired on the 3rd of the month

Use this when

• A budget alert fires within the first days of the month while spend looks normal.
• The budget's cost type is set to forecasted rather than actual.
• The team has started ignoring the alert because it "always fires."

Not for this skill when

• The alert tracks actual spend and still fires early. That is a real overspend or a bad baseline.
• You want a forecast warning on purpose. That needs a separate budget with a lower threshold.

Steps

1. Open the budget and check the cost filter: forecasted vs actual. Verify: it says forecasted.
2. Change the 100% budget to actual spend: aws budgets update-budget with CostTypes set to actual, or edit in the console.
3. Create a second budget for the forecast: same amount, threshold at 80% of forecasted spend, alert labeled clearly as "early warning."
4. Point the two alerts at different severities: actual-100% pages, forecast-80% sends a low-priority note.
5. Note the forecast lag: the forecast needs a few days of data each month to calibrate, so expect a noisy first week.

Variant phrasings

aws budget forecast alert fired on day 3

Symptom-level search.

forecasted vs actual spend budget alert

The configuration question behind it.

budget alert always fires at start of month

How teams describe it after muting it twice.

Compatibility: AWS Budgets; forecast data requires enough historical spend for the model to train on.

Why it happens

Forecasted spend for the month is projected from partial data and then compared against the full-month budget. On day 3 the model often extrapolates noise, so "100% of forecasted" trips while actual spend sits at 10%. Agents pick "forecasted" because it sounds smarter; it just fires sooner.

Edge cases / pitfalls

• Do not delete the forecast budget. An 80% early warning is genuinely useful when it is labeled as one.
• Forecast accuracy is worst for spiky workloads. If the early-warning budget is noisy, raise it to 90% rather than deleting it.
• Actual-spend budgets have evaluation lag too. A 100% actual alert still lands hours after the breach, not instantly.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Dc3Tc1KxQabSflvXwwm67g