Hi, xianfeng.
I see how convenient it is to use a fixed monthly exchange rate to maintain stability in managing currency conversions or foreign sales.
Currently, QuickBooks Online does not have this functionality because exchange rates change daily. The system is designed to use daily rates that align with accounting standards in most regions.
While you can manually update the exchange rate for each transaction with your preferred fixed monthly rate, there is no option to automatically apply the same fixed rate to all transactions for a specific period, like a month. This means you would need to update the rate manually for each transaction.
Please let us know if you have additional questions or QuickBooks-related concerns. The Community team is always available to provide the necessary help.