Standard mortgage contracts include periodic debt repayment plans (amortization schedules) designed to build-up illiquid savings in the form of home equity, which can be substantial even from a macroeconomic standpoint. For example, U.S. households invest hundreds of ($) billions each year in mortgage amortization plans – comparable in size to pension program contributions. We provide the first empirical evidence on the causal effects of mortgage amortization on wealth accumulation. Ex-ante, effects are unclear. If increased debt repayments crowd-out households’ non-mortgage savings, rather than alter their consumption/labor supply, there would be no effect on wealth. We use individual administrative data and plausibly exogenous variation in the timing of home purchases surrounding an interest-only mortgage reform in the Netherlands. We find little-to-no change in the accumulation of non-mortgage savings, even four years later, despite a significant increase in debt repayment. This lack of crowding-out implies a surprising near 1-for-1 rise in net worth and little savings-debt fungibility, financed via increased labor supply and reduced expenditures. Results hold using life-events (ex. birth of a child) as an instrument for the timing of home purchase, and appear unaffected by potential selection or confounded treatment concerns. Effects also hold focusing on buyers with substantial liquid savings and across the spectrum of ages, suggesting general applicability beyond just non-savers and the young. Our findings suggest that homeownership, when coupled with amortizing mortgages, is a key driver of household wealth building and inequality, and that the amortization-wealth elasticity is a crucial consideration for macroprudential policies.