This paper presents a financial model developed to project the future interest expenses of a large set of rolling debt instruments. It aims at forecasting the financial consequences, for borrowing entities, of changes in the interest rate environment. Starting from detailed data on the current debt's maturity structure and interest rates, and given a future path for market interest rates, we simulate the progressive repayment of borrowed amounts refinanced by issuing new debt at prevailing conditions, with few structural assumptions. The model simulates the effect of variable-rate interests and inflation indexing. It can handle any joint future trajectory of outstanding amounts and interest rates, as represented by a full yield curve structure. […]