It is very easy to model utilizing your HSA account to fund your healthcare expenses in the Planner.
STEP 1: Head over to My Plan > Money Flows
STEP 2: Scroll down to Transfers
STEP 3: Press "Add a Transfer"
STEP 4: Enter a transfer from the HSA account to the after-tax account with the lowest growth rate. This account has priority for funding expenses in the Planner.
Please see our article on funding expenses for more information.