The break-even calculation runs the same month-by-month simulation as the Rent vs Buy Calculator, extended to a 30-year horizon. The break-even point is the first year where cumulative buying costs (including the down payment, closing costs, mortgage payments, taxes, insurance, maintenance, and HOA) fall below cumulative renting costs (rent payments and renters insurance).
The upfront cost disadvantage of buying is overcome over time through two mechanisms: home equity builds as mortgage principal is paid down, and rent payments compound while the mortgage payment stays fixed. The break-even point is earlier when home appreciation is high, rent growth is fast, or the down payment percentage is high.
Related reading: How long should you stay in a house to make buying worth it?