The house price-to-income ratio (PIR) is widely used as an affordability indicator. This paper complements the cross-sectionally focused literature by proposing a tractable model for the PIR dynamics. Our model predicts that the PIR is very persistent and is correlated to the lagged aggregate output. Cross-country analysis confirms this prediction and provides evidence for a long-term, positive and significant relationship between PIR and aggregate production. Our results hint at the construction of an early warning system for housing market mispricing. Our tractable formulation of a stochastic money growth rule may carry independent research interest.