Rent, and when it stops

Rent used to be something you folded into living expenses. It is now a line of its own, because two questions need it separately:

• What does the plan cost while you rent?
• Would you be better off renting than buying? — the crossover view compares the plan you have against the same plan that never buys, and that comparison is meaningless if rent is buried in another number.

What the engine does

• Charges the rent every month between its start and its end.
• Grows it once a year, the way a lease renews, at its own growth rate. Leave the rate blank and it follows the plan's inflation; set it to zero to freeze it in nominal terms.
• Ends it at the first home purchase by default. A month either pays rent or carries a home; charging both is the modelling error this rule exists to prevent, and it is the one that quietly makes buying look worse than it is.
• Reports it on every month and year row, so the yearly table can show it beside housing.

What to do if you would keep renting

Give the rent an explicit end date. An explicit date always wins over the default — someone who buys a home to move into later, or who sells and goes back to renting, is a plan the engine must not overrule. The warning tells you the default applied so the choice is yours rather than ours.

What it deliberately does not model

A rent that changes for a reason other than annual growth — a move, a roommate leaving, rent control ending — is not modelled. Use two plans and compare them, or set the growth rate to the average you expect over the horizon.