Overview

DDM has two billing modes: yearly/monthly and pay-per-use.

Yearly/Monthly is a prepaid billing mode. You pay in advance for a subscription term, and in exchange, you get a discounted rate. The longer the subscription term, the bigger the discount. Yearly/Monthly billing is a good option for long-term, stable services.
Pay-per-use is a postpaid billing mode. You pay as you go and just pay for what you use. DDM instance usage is calculated by the second but billed every hour.

**Table 1** Differences between billing modes
Billing Mode	Yearly/Monthly	Pay-per-use
Payment	Prepaid Billed by the subscription term you purchase	Postpaid Billed for what you use
Billed Usage Period	Billed by the subscription term you purchase	Calculated by the second but billed every hour
Billing Items	Instance specifications (vCPUs and memory) and EIP	Instance specifications (vCPUs and memory) and EIP
Changing the Billing Mode	Yearly/Monthly can be changed to pay-per-use. The change takes effect only after the yearly/monthly subscription expires.	Pay-per-use can be changed to yearly/monthly.
Changing the Specifications	Supported	Supported
Application Scenarios	Recommended for resources expected to be in use long-term. A cost-effective option for scenarios where the resource usage duration is predictable.	Recommended when the resource demands are likely to fluctuate and you want more flexibility.