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Azure Reservations explained

Azure Reservations exchange a one- or three-year commitment for discounted eligible usage. The safe purchase amount comes from a durable hourly baseline after rightsizing, existing commitments, scope, region, family flexibility, planned migrations, and business risk are considered. A reservation is a billing decision, not proof that capacity is required.

Costframe practical guide · 3 min read

Review the uncovered hourly baseline

Coverage is not utilization

01

Coverage

Eligible usage receiving a reservation benefit ÷ total eligible usage. Low coverage can indicate opportunity, but not the safe purchase quantity.

02

Utilization

Reserved hours used ÷ reserved hours purchased. Low utilization means the commitment is not being fully consumed.

03

Baseline

The lower, durable band of eligible usage that persists across weekdays, weekends, releases, and seasonal periods.

04

Sequence

Remove waste and right-size first; otherwise a commitment can lock in capacity the team should have removed.

A procedure with accountable owners

  1. 1 / Normalize eligible usage

    Group by benefit-relevant scope, region, family, meter, and hour; account for current reservations and savings plans.

    Owner
    FinOps
    Cadence
    Before purchase
    Verify
    Eligible hours reproduce provider analysis.

  2. 2 / Model a conservative baseline

    Use a representative window and subtract known retirements, migrations, rightsizing, and seasonal peaks.

    Owner
    FinOps + engineering
    Cadence
    Quarterly
    Verify
    Baseline persists across the chosen window.

  3. 3 / Compare terms and flexibility

    Evaluate term, payment option, scope, exchange/cancellation terms, and opportunity cost.

    Owner
    Procurement + finance
    Cadence
    Per purchase
    Verify
    Scenario is reviewed against current provider terms.

  4. 4 / Monitor after purchase

    Track utilization and coverage separately; investigate drift before buying more.

    Owner
    FinOps
    Cadence
    Weekly
    Verify
    Unused commitment has an owner and corrective plan.

Illustrative usage coverage

Eligible usage in one normalized group
10,000 instance-hours
Usage receiving reservation benefit
6,000 instance-hours
Coverage
6,000 ÷ 10,000 = 60%
Uncovered usage
4,000 instance-hours; not a purchase quantity

Hypothetical usage from one eligibility group, not customer results. The uncovered hours may be scattered peaks. Review their hourly pattern before buying. Costframe's modeled reservation-gap finding is not a measurement of your actual benefit coverage.

Separate a commitment benefit from a capacity decision

Check reservation utilization and coverage separately. Utilization describes how much of the purchased benefit was used. Coverage describes eligible usage receiving that benefit. A gap in coverage does not establish a safe purchase quantity; planned retirements and migrations can reduce future eligible demand.

Compare the cash view with the allocation view. Actual cost can show a purchase in its billing period, while amortized cost spreads the commitment across its term and applicable usage. Record which basis supports the analysis and use that same basis for the comparison.

Your next task

Review the uncovered hourly baseline

Take one eligible region and VM family. Separate already-covered hours from the remaining demand, then remove planned retirements and rightsizing. Bring the conservative baseline and current purchase terms to finance; do not purchase the entire monthly coverage gap.

Review a reservation coverage gap

What not to do

  • ×Buying against a monthly average instead of hourly baseline
  • ×Treating low coverage as an automatic purchase signal
  • ×Ignoring planned migrations and rightsizing
  • ×Mixing utilization and coverage into one KPI

Sources and further reading

Microsoft: Azure Reservations overview

Actual and amortized cloud cost

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