MANY home buyers align themselves with real estate agents who, while touring a home, can help to calculate a mortgage payment based on various negotiating strategies.

Now, with the proliferation of software applications for iPhones and BlackBerrys, these on-the-fly calculations can be replaced by more precise calculations. And the software programs are quite cheap, typically starting at $1.

For those looking to refinance a loan, free online calculators offered by lenders and real estate companies might suffice. But for home shoppers, a mobile mortgage calculator brings instant and precise information to the process. Such aids certainly have become more commonplace.

David Daniels, a senior sales associate with the Corcoran Group, recalled seeing a young man tapping away on his BlackBerry last month, while his wife discussed possible sale prices for condominiums at Windows on 123, in Harlem. “At first I thought he was just answering e-mails,” Mr. Daniels said. “But they were actually figuring out different scenarios of how much money to put down, and what their payment would be.

“It’s much better as a buyer to see those numbers generated with your own calculations, rather than asking a broker who might guesstimate,” he added.

Toni Habetz, an agent at Prudential Connecticut Realty, said that she had also observed clients using mobile mortgage calculators during house tours.

“Clients aren’t as forthcoming about how much financial information they divulge,” she said. “And now they don’t have to, because they can figure out the mortgage information for themselves.”

These new applications are fairly straightforward calculators, but they can also include other information and features to help aid the mortgage decision.

Take, for instance, the Mortgage Calculator Pro ($8 for BlackBerry users). After users enter a mortgage amount, interest rate, taxes, property insurance fees and preferred loan term, the program displays monthly payments.

It also supplies comparative results. The purple color-coded data refer to a submitted loan term, while orange results show what users would pay in interest and total loan payments for the life of the loan, if they instead choose different loan terms.

Less helpful, but still interesting, is a feature that lets users type in a desired monthly payment and interest rate, and then determines how long it would take to pay off the mortgage.

There is no way to provide a precise calculation, however, for those who will have to have private mortgage insurance, because they are not planning to make a down payment of at least 20 percent.

Mortgage insurance rates vary so much that such calculations would be unreliable, said Gregory Raiz, the president of the Raizlabs Corporation in Brookline, Mass., which produces the Mortgage Calculator iPhone and iPod touch application ($1). The Mortgage Calculator is a good example of how the simpler mobile applications work. With sliders and data-entry fields, the software determines the monthly payment on a single screen.

The program also allows users to type in the square footage of the property, for comparing different homes. Users may send the results of the calculation to themselves, with notes, as e-mail messages.

There are dozens of other mortgage calculators available for iPhones, including the Mortgage Calculator Pro from SVT Software, the CalcsPro-Mortgage Calculators from Mortal Geek and Recalc from Anil Bajaj.

These applications will have a limited impact, at least in the current market, according to Thomas Vanderwell, a mortgage officer at a bank who blogs at Straighttalkaboutmortgages.com about real estate.

“Anytime you can have exact information rather than ballpark information, that’s a good thing,” Mr. Vanderwell said. “But in the last six to nine months, most buyers are cautious, and they don’t move so fast that they need that information when they’re looking at the house.”