The right Azure commitment coverage target is your steady state usage floor, the capacity that runs every hour of every month, not a round number picked from a slide. Cover that floor with reservations and the Azure Savings Plan, leave the variable layer on demand, and your effective rate falls without stranding spend on capacity you stop using. Coverage strategy is risk adjusted, not discount maximised.
This sits in the Azure compute and reservations cluster. The mistake to avoid is chasing a high coverage percentage as if it were the goal; the goal is the lowest risk adjusted cost, and that usually means covering less than all of your usage.
Why a coverage percentage is the wrong starting point
A target like 80 percent coverage sounds disciplined but it is arbitrary unless it maps to your usage shape. Two estates with the same spend can have very different floors: one runs a stable baseline every hour, the other spikes hard during business hours and idles overnight. Committing the same share of both strands money on the spiky one. Start from the shape, not the percentage.
Find the steady state floor
The floor is the level of usage that is present continuously across the period, reconciled against your Azure cost exports. Plot hourly compute usage over a representative few months and look for the line everything sits above. That floor is the spend that is safe to commit, because it will be there for the full term regardless of how the variable layer moves.
Everything above the floor is variable, and variable usage belongs on demand or on the more flexible Azure Savings Plan, not on a deep reservation you might not fully use.
Blend reservations and the Azure Savings Plan
The two instruments trade discount for flexibility, and a sensible book uses both.
| Layer | Instrument | Why |
|---|---|---|
| Stable, specific usage at the floor | Reservations | Deepest discount on capacity you know will run |
| Steady but shifting across families or regions | Azure Savings Plan | Trades a little discount for flexibility as the mix changes |
| Variable, spiky, or uncertain | On demand | No commitment risk on capacity that may not recur |
A European SaaS company had committed to a flat coverage target across all compute and was carrying underused reservations on a workload that idled overnight. We rebuilt coverage from the hourly floor, moved the shifting layer to the Azure Savings Plan, and left the overnight variance on demand. Effective rate improved and the underused commitment disappeared. Figures are verified against billing data and anonymised.
Manage the downside
If you over commit, you pay for capacity you do not use, which can erase the discount entirely. Reservations can be exchanged or, within limits, refunded, but the cleaner answer is to size coverage to the floor so over commitment does not happen. Review coverage on a quarterly cadence against an updated forecast, and ladder terms so no single expiry forces a rushed decision.
Frequently asked questions
What is a good reservation coverage target on Azure?
Should you use reservations or the Azure Savings Plan?
What happens if you over commit on Azure?
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