Sustained use discount (SUD)
A sustained use discount (SUD) is a discount Google Cloud applies automatically to some Compute Engine resources that run for more than 25% of a month. The longer they run, the lower the rate for the remaining hours, up to 30% off for a full month on eligible machine series, with no commitment.
In plain English
Think of a coffee shop loyalty card that fills itself in. Nothing to sign up for: the more days you come in this month, the cheaper each further cup gets. On the first of the month, the card resets.
Formula and worked example
SUD = on-demand cost − SUD-adjusted cost
- On-demand cost
- = hours the resource ran × on-demand rate
- Quarter rates
- = 100%, 80%, 60% and 40% of the on-demand rate for the first, second, third and fourth 25% of the month (30% tier)
- SUD-adjusted cost
- = hours in each quarter of the month × that quarter's rate
| First 25% of the month (182.5 hours) at 100% | $18.25 |
|---|---|
| Second 25% at 80% | $14.60 |
| Third 25% at 60% | $10.95 |
| Fourth 25% at 40% | $7.30 |
| Cost after the sustained use discount | $51.10 |
| Discount versus $73.00 on demand | 30% |
Run the same instance for only half the month and it gets just the first discounted quarter: $18.25 + $14.60 = $32.85 instead of $36.50, a 10% discount.
Why sustained use discounts matter
SUDs are a discount you don't have to buy: Google Cloud applies them automatically, with nothing to commit to or manage. For steady workloads on eligible machine series, they lower the bill with no risk of unused commitment.
They also change the maths of commitments. Usage covered by a committed use discount does not also get a sustained use discount, so the real gain from a CUD on an eligible series is the CUD discount minus the SUD you were already getting. On series without SUDs, such as E2, commitments are the main way to lower the price of steady usage.
Common mistakes
- Counting SUDs as commitment savings. SUDs happen with or without a commitment. When you judge a CUD, compare it with the SUD-adjusted cost, not the full on-demand price, or the CUD looks better than it is.
- Expecting them on every machine type. E2 and some other machine series don't get sustained use discounts. Check the series before you plan around them.
- Forgetting the monthly reset. The discount builds up within each calendar month and starts again on the first. A resource that runs for the second half of one month and the first half of the next gets only a small discount in each.
- Leaving the discount line out. The SUD shows on the bill as its own line. Analysis that drops it overstates Compute Engine cost; analysis that subtracts it twice understates it.
Where to find it in AWS, Azure and Google Cloud
| Cloud | What it is called | Where to find it |
|---|---|---|
 AWS | No equivalent | AWS has no automatic discount for running longer. The closest options, Savings Plans and Reserved Instances, need a commitment. |
 Azure | No equivalent | Azure has no automatic discount for running longer. Reservations and savings plans for compute need a one- or three-year commitment. |
 Google Cloud | Sustained use discounts | Applied automatically to eligible Compute Engine resources: up to 30% for N1 and up to 20% for N2 and N2D, none for E2. The discount appears on the bill as a separate line combining all eligible usage in the Cloud Billing account. |
How CloudYali helps
CloudYali reads Google Cloud cost from your Cloud Billing export to BigQuery, which records sustained use discounts with the rest of your credits, and shows Google Cloud CUDs in Financial Commitments next to AWS and Azure commitments.
Related terms
Commitments & rates
Committed use discount (CUD)
A committed use discount (CUD) is Google Cloud's commitment discount: you commit to a set amount of resources, such as vCPUs and memory in one region, or to an hourly spend, for one or three years, and pay lower prices on that usage. The commitment is billed every month of the term, used or not.
Billing & cost types
On-demand price
On-demand price is the public, pay-as-you-go price for cloud usage with no commitment: you pay per second, hour, gigabyte or request for what you use. It is the baseline that every commitment discount, and metrics such as coverage and effective savings rate, are measured against.
Commitments & rates
Commitment coverage
Commitment coverage is the share of commitment-eligible usage that a Reserved Instance, Savings Plan, Azure reservation or Google Cloud committed use discount paid for, measured at on-demand prices. The rest was billed at full on-demand rates, so low coverage on steady usage is money left on the table.
Commitments & rates
Effective savings rate (ESR)
Effective savings rate (ESR) is net savings as a share of what all commitment-eligible usage would have cost at on-demand prices. Because it subtracts commitment you paid for but didn't use, it is the one rate-optimization number that buying too many Reserved Instances, Savings Plans or committed use discounts can't inflate.
Frequently asked questions
Do you need to do anything to get sustained use discounts?
No. Google Cloud applies them automatically to eligible resources once they run for more than 25% of the month, and they show on the bill as a separate line.
Do sustained use discounts stack with committed use discounts?
No. Usage covered by a CUD doesn't also get a sustained use discount. Usage above the commitment is billed at on-demand rates and can earn a SUD.
Which machine types get sustained use discounts?
Among general-purpose machines, N1 gets up to 30% and N2 and N2D up to 20%; E2 gets none. Check Google's list of eligible resources for other series, GPUs and sole-tenant nodes.
