Why can I only schedule a tax payment within a fixed period each month?

This is to allow IRAS sufficient time to process each payment, and to prevent any potential reconciliation issues with your payments. For users with existing GIRO payment plans, we would require 3-5 business days before your existing GIRO deduction takes place on a certain date every month. Once the GIRO deduction takes place, IRAS would require another 3-5 business days to update your Statement of Account with the outstanding tax balance, as seen in your myTax Portal account.