Generally, financial institutions will immediately deduct the applicable withholding tax based on the amount of each withdrawal. Because withdrawals are fully taxed as income on your income tax return, the amount of the withholding tax may be less than what is owed on the total amount withdrawn in one year.
Your financial institution may apply the withholding tax based on the total amount of multiple withdrawals depending on how often you make them. Speak to your financial institution to learn more about making multiple RRSP withdrawals, and track your withdrawals throughout the year to ensure you are aware of the additional amount you may owe when you file your annual income tax return.
Learn more about making withdrawals from your RRSP before you retire.