Using a novel source of quasi-experimental variation in interest rates, we develop a new approach to estimating the Elasticity of Inter-temporal Substitution (EIS). In the UK, the mortgage interest rate features discrete jumps — notches — at thresholds for the loan to value (LTV) ratio. These notches generate large bunching below the critical LTV thresholds and missing mass above them. We develop a dynamic model that links these empirical moments to the underlying structural EIS. The average EIS is small, around 0.1, and quite homogeneous in the population. This finding is robust to structural assumptions and can allow for uncertainty, a wide range of risk preferences, portfolio reallocation, liquidity constraints, present bias, and optimisation frictions. Our findings have implications for the numerous calibration studies that rely on larger values of the EIS.