Banking on assumptions? How banks model deposit maturities

How do banks manage the behavioural maturity of non-maturing deposits (NMDs)? Using a rich and confidential dataset, we investigate how banks model deposit maturities based on internal assumptions. Although NMDs are contractually floating-rate liabilities with zero maturity, banks reallocate them across different maturity buckets using models that reflect past customer behaviour. Notably, only 20% of NMDs are treated as having zero maturity, while about 10% are assigned maturities beyond seven years. We assess whether these modelling assumptions align with banks’ deposit structures. Results show that banks with more volatile, interest rate-sensitive, and digitalised deposit bases tend to assign shorter maturities, appropriately reflecting underlying risks. However, during the recent monetary policy tightening, banks with more sensitive NMDs did not shorten assumed maturities or update models. These findings underscore the critical importance of timely and accurate calibration of NMD assumptions to support effective asset-liability management and preserve financial stability. JEL Classification: E51, E52, G21