Rent-versus-buy is not a contest between rent and the mortgage payment. It is a comparison of two balance sheets and two cash-flow paths over a stated period—with transaction costs at the edges and uncertainty throughout.
Time changes the cost of entering and leaving
Buying can require property transfer tax and other closing costs; selling can involve material transaction costs. A shorter holding period gives those one-time costs fewer years over which to spread. The model should make the horizon an explicit input, not bury it inside a conclusion.
Give both sides their capital
The owner builds equity through principal repayment and changes in home value. The renter retains the down payment and closing cash and may invest the difference between the two monthly costs. A fair comparison carries both portfolios forward using disclosed assumptions.
Run a range, not a verdict
Test flat, adverse, and favourable cases for home value, rent, investment return, and recurring owner costs. Then record mobility, tenure security, renovation freedom, school or care needs, and repair tolerance separately. A deterministic tool can reveal the assumptions driving the result; it cannot decide the household’s values.
Compare both balance sheets over your actual horizon.
No provider paid to appear in this issue. The examples explain public information and deterministic scenarios; they do not confirm eligibility, predict a property outcome, or replace transaction-specific professional advice.