This presentation is an early stage proposal. Despite the recent monetary tightening, house prices in the US have so far been resilient. This paper studies the impact of mortgage lock-in on house prices through the lens of a quantitative life-cycle model with endogenous house prices. Household income and homeownership features a hump-shaped pattern with respect to age — households rent when young, purchase houses in middle age, and downsize in old ages. I calibrate the model to a no inflation stationary equilibrium (reflecting pre-covid markets) and simulate transition path under an MIT shock of surprise inflation and interest rate increases. Higher mortgage rates lower housing demand from young households, but prices remain stable because older households delay downsizing due to locked-in low mortgage rates.