In most places in the U.S., it’s still cheaper to buy a home than rent one. If you buy a home with a traditional 20 percent down payment and a 30-year mortgage, on average it will cost about one-third less than renting a similar home around the U.S., according to a new report from Trulia, a real estate site.

Trulia says there are two reasons why home ownership is now so affordable. One is cheaper mortgage rates, which have decreased from 4.5 percent in 2014 to 3.87 percent as of April 15. Another is that the growth in home prices over the last year -- 3.9 percent -- wasn't much larger than the 3.7 percent gain in rents.

But while it's cheaper to buy than rent on a national basis, in some cities it can be a tougher call. In particular, Trulia says there is not much difference in renting and buying in Honolulu, HI; San Jose, CA; Lancaster, PA; Sacramento, CA; and San Francisco. Buying a home is the more obvious choice in Sarasota, FL; Fort Myers, FL; Baton Rouge, LA; New Orleans; and Miami, where it costs 50 percent less or more to buy than rent.

Trulia bases these calculations on all the homes listed on their site for rent or sale in March 2015. They include things like mortgage payments, maintenance, insurance, taxes, closing costs, down payment, sale proceeds and security deposits in the cost of owning and renting, and make a separate calculation for homeowner association fees. Their calculations also assume buyers itemize their federal tax deductions, are in the 25 percent tax bracket, and will stay in their home for seven years. Here's what those assumptions look like:

If these assumptions are different for you, that may change the renting or buying calculus. You can test that out with the interactive version of this map or Trulia's rent vs. buy calculator.

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