Mortgage at retirement

Pay minimum: the engine continues making the scheduled mortgage payments from retirement cashflow. No extra principal.

Pay it off at FIRE: the engine treats this as 'prepay with surplus'. Each retirement year, any cashflow surplus above the planned drawdown goes to extra mortgage principal until the loan is cleared. Not a lump-sum payoff at the retirement date.

Use super lump sum at preservation age: the engine continues minimum payments through the bridge years, then at pension-phase start (retired AND past preservation) withdraws from super to clear the remaining mortgage balance in one go. Tax-free for members over 60. If super is not enough to clear the loan, a warning is surfaced at end-of-run.

Some users pay it off at FIRE because they want to enter retirement debt-free for psychological comfort.

Some users continue the minimum because the mortgage rate is below their expected investment return, so the spread compounds in their favour.

Some users wait for preservation age because they want non-super to fund the bridge years and use super for the lump sum payoff.

Pay-off-at-FIRE (prepay with surplus) absorbs cashflow that would otherwise compound in non-super. On marginal-bridge profiles this can flip the projection from sustainable to not.

Continuing minimum payments means retirement cashflow needs to cover the mortgage, which raises the projected drawdown each year.

Use-super-lump-sum at preservation age is operationally simple but locks you into the mortgage rate during the bridge years even if rates fall, and the lump-sum withdrawal can be a meaningful chunk of super depending on the loan balance at that point.