Afaict, the 30% rule of thumb has been quoted for a long time, but originated in an era when the main household costs were considerably different in other respe

Afaict, the 30% rule of thumb has been quoted for a long time, but originated in an era when the main household costs were considerably different in other respects as well. The classic mid-20th-century rule in the U.S. was 60% of your expenses on housing+food, split about half and half. Nowadays the split is nowhere near half-and-half between those, in part because food has gotten much cheaper. It's sort of interesting to see the historical consumer spending breakdowns: http://www.bls.gov/opub/uscs/home.htm http://www.bls.gov/opub/uscs/home.htm