We provide the first economic research on `buy now, pay later' (BNPL): an unregulated FinTech credit product enabling consumers to defer payments interest-free into instalments. In 2021 transactions by BNPL firms are charged $19.5\%$ of active cards in our UK data. Charging a $0\%$ interest, amortizing debt cards, where typical interest rates $20\%$ and amortization schedules decades-long, rais...