SLO Measurement Window: 30 Days vs 7 vs 90
The window choice changes the SLO’s personality. Pick to match your business cadence and on-call appetite.
What the window actually controls
The window decides ‘how much budget you have at any moment.’ A 30-day window with 0.1% budget = 43 minutes of bad per month.
Shorter window = less budget, faster reaction. Longer = more budget, slower.
Four common windows
- 7-day: sensitive; tight feedback loop.
- 30-day: standard; quarterly business cadence.
- 90-day: generous; long-tail trends.
- Annual: contract-aligned; rare for engineering use.
Rolling vs fixed
Rolling: window slides; budget refreshes daily.
Fixed: window resets at month/quarter end; budget refills cliff-style.
Rolling avoids cliff drama; fixed aligns to billing.
Picking by business cadence
Match window to action cadence. If action is monthly, use 30-day rolling. If action is sprint-based, 14-day might fit.
The window is a tunable; revisit annually.
Antipatterns
- 7-day window for noisy services. Always burning.
- Annual window for engineering. No actionability mid-year.
- Mixed windows in same dashboard. Confusing.
What to do this week
Three moves. (1) Apply the pattern to your most-impactful service. (2) Measure adherence for 30 days. (3) Rewrite the policy or the SLO if the gap is durable.