This topic describes how you are charged for configuration changes of payasyougo and subscription clusters.
Payasyougo
Payasyougo clusters are charged on an hourly basis. After you change the configurations of a payasyougo cluster, the cluster is charged at the new price on an hourly basis.
Subscription
Change type  Description 

Upgrade specifications or add nodes  Fees = Total fees of the new configurations for the remaining subscription period
 Total fees of the original configurations for the remaining subscription period.
Total fees of the new configurations for the remaining subscription period is calculated
based on the following formula: Monthly price of the new configurations/30/24 × Remaining
subscription period measured in hours. Total fees of the original configurations for
the remaining subscription period is calculated based on the following formula: Monthly
price of the original configurations/30/24 × Remaining subscription period measured
in hours.
For example, the monthly price of the new configurations is USD 14,400. The monthly price of the original configurations is USD 7,200. The remaining subscription period is 50 days. The payment is calculated based on the following formula: (USD 14,400/30/24 × 50 × 24)  (USD 7,200/30/24 × 50 × 24) = USD 12,000. 
Downgrade specifications or delete nodes  Refund = Total fees of the original configurations for the remaining subscription
period (Monthly price of the original configurations/30/24 × Remaining subscription
period measured in hours)  Total fees of the new configurations for the remaining
subscription period (Monthly price of the new configurations/30/24 × Remaining subscription
period measured in hours).
For example, to purchase a subscription cluster for three months, you are charged USD 3,500. You pay USD 3,000 for the cluster after you use coupons. After two months, the total fees of the original configurations for the remaining subscription period become USD 1,000. The total fees of the new configurations for a month are USD 800. The refund is calculated based on the following formula: USD 1,000  USD 800 = USD 200. Note The system refunds fees for the downgraded configurations of a subscription cluster.
However, the system does not refund fees for the entire cluster. If you want to use
this service, Submit a ticket. If your application is approved, your subscription cluster is frozen and will be
deleted after 14 days.

FAQ
Why is my received refund less than the refund that I calculated for the downgraded configurations of the cluster?
Check the following scenarios before you downgrade the cluster configurations:
 You are offered discounts for the order of the original configurations. For example, if you purchase the cluster on the International site (alibabacloud.com) and the subscription period is one year or longer, you are offered a 15% discount.Assume that the original price of the cluster is USD 1,000 and you pay USD 850 for the cluster. If you downgrade the cluster configurations, USD 850 is used as the payment amount to calculate the refund of the downgrade.
 Assume that you use coupons for the order of the original configurations and you pay USD 500 for the order. If you downgrade the cluster configurations, USD 500 is used as the payment amount to calculate the refund of the downgrade.
References
PolarDB for PostgreSQL: Change specifications