In Hong Kong, 35% of residential mortgage loans are adjustable rate mortgages with variable tenor (VRT). That is, with a change in interest rates, the loan adjusts its maturity and principal payment such that the monthly installment remains the same. In other words, instead of bearing a volatility on monthly payments as in a fixed-tenor variable payment (VRP) mortgage, VRT mortgagors bear interest rate risk by bearing a tenor risk. In this paper, we analyze the valuation of this type of mortgages and the results are compared with the conventional VRP mortgages. We find VRT loans are less expensive from a borrower's perspective than VRP loans, but the difference between the loans becomes less significant if a tenor cap is added to the VRT loan.