Practical guide
Calculate a Compute Engine committed use discount break-even
Compare a steady eligible Compute Engine baseline with a one- or three-year commitment without treating a discount as guaranteed savings.
Updated · Sources checked
Commit only the durable baseline
A Compute Engine committed use discount (CUD) makes sense when eligible usage is expected to persist for the selected term. Google offers one- and three-year commitments, and documents both resource-based and compute-flexible forms. The central question is not the advertised discount: it is whether the commitment stays utilized hour after hour.
Use a simple hypothetical comparison. A team has $100 of eligible On-Demand usage every month and expects a 30% discounted commitment price. At full utilization, the modeled commitment charge is $70 and the apparent monthly difference is $30. If only $50 of eligible workload remains, the team still owes the commitment charge but receives only $50 of matching workload value; the unused portion erodes the saving. Enter the actual hourly commitment and expected eligible spend, not this example’s rate.
Match the commitment type to the workload
Resource-based CUDs cover a minimum amount of specified eligible resources in a region. Compute-flexible commitments are spend based and can cover eligible Compute Engine use and, under the documented rules, eligible GKE and Cloud Run spend. Those details matter when services share a billing account. A commitment is distinct from a reservation: it gives discounted pricing, while a reservation addresses zonal capacity.
Google applies commitments on an hourly basis. Discount programs are mutually exclusive in the documented order, so do not stack sustained-use and CUD percentages in a spreadsheet. Check the machine family, region, operating system, licenses, GPUs, and other SKU eligibility before signing.
A conservative workflow
Take 3–6 months of hourly billing export data, find the lowest sustained eligible baseline, and model only that amount. Keep volatile growth, experiments, and interruptible work On-Demand or Spot until usage becomes durable. Recalculate when a migration, machine-family change, or region change alters eligibility.
Use the Compute Engine Committed Use Discount Calculator to test utilization and term assumptions alongside the Compute Engine cost calculator.
FAQ
Can I cancel a resource-based commitment?
Google says an active purchased commitment cannot be cancelled or deleted before its term ends.
Does a CUD cover every project cost?
No. It covers only eligible usage. Storage, network, and unsupported SKUs remain separate.
Official sources
- https://cloud.google.com/products/compute/pricing
- https://cloud.google.com/compute/docs/instances/committed-use-discounts-overview