Cloud pricing term
What is a burstable vCPU?
A burstable vCPU can run above a baseline for limited periods by spending accumulated CPU credits or by entering a paid surplus mode.
The expensive mistake
Sizing a continuously busy service from the advertised vCPU count and ignoring the baseline, credit mode, and surplus price. Once credits are exhausted, the instance can fall back to baseline performance or continue bursting with extra charges, depending on the provider and mode.
Where it appears on your bill
The instance itself appears as normal compute. Paid surplus may appear as CPU credit or surplus-credit charges; throttling may change performance without adding a line.
Worked example
The dated example calculates AWS t4g.nano compute at $0.0042 x 730 = $3.07/month. AWS lists T4g Unlimited surplus at $0.04 per vCPU-hour. Ten surplus vCPU-hours add 10 x $0.04 = $0.40, bringing compute to $3.47 before EBS, IPv4, and transfer.
Example prices checked: