Overview

There are yearly/monthly and pay-per-use billing modes. Each one has different advantages and disadvantages.

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. A pay-per-use NAT gateway can be billed by day or by hour. This mode allows you to adjust resource usage easily. You do not need to prepare resources in advance, and will not have excessive or insufficient preset resources.

**Table 1** Differences between billing modes
Billing Mode	Yearly/Monthly	Pay-per-use
Payment	Prepaid Billed by the subscription term you purchase.	Postpaid Billed by the usage duration
Billing Method	Billed by the subscription term you purchase.	Billed by day or hour (calculated by the second but billed every hour)
Billing Items	NAT gateway type and specifications	NAT gateway type and specifications
Changing the Billing Mode	Yearly/Monthly can be changed to pay-per-use. The change takes effect only after the yearly/monthly subscription expires. For details, see Yearly/Monthly to Pay-per-Use.	Pay-per-use can be changed to yearly/monthly. For details, see Pay-per-Use to Yearly/Monthly.
Changing the Specifications	Public NAT gateway can only be upgraded to a gateway of more robust specifications.	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.