For a homeowner whose mortgage has become unaffordable because of a lost job, an interest-rate reset, or some other reason, the prospect of getting the loan’s terms modified sounds good—but the process can be confusing and dispiriting. That’s why a California company led by a veteran mortgage banker has devised the Homeowner Toolbox, an online guide to the preparation of an application for a “loan mod.”

The site provides all the forms, calculations, and letters you will need to pull together an application. That includes a cover letter to your lender in which you state why you need a loan modification (layoff, health crisis, etc.), as well as a detailed worksheet of your family’s income and expenses. That part helps determine the likelihood of your being approved, and it’s tailored to the specific requirements of any of a few dozen mortgage lenders. Once you indicate which lender holds your mortgage, the site’s “Probability Meter” lets you know how likely you are to get approved for a modification. (That is, if your lender isn’t planning to sit it out until you wind up in foreclosure, which, as the Washington Post reported Tuesday, is sometimes a better deal for the lender.)

If your chances of getting a loan mod are not good, the Homeowner Toolbox might suggest ways to make your financial profile more appealing. For example, while an adult child paying a parent rent for part of the parent’s home doesn’t usually qualify as income on a conventional mortgage application, it often does in a loan mod, according to Andy Firoved, the company’s CEO.

The site can also suggest such fixes as trimming household expenses. “We’ve seen people get declined for being as little as $10 [a month] off of having enough to cover the [modified] loan,” Firoved says.

To get a loan mod, the homeowner often has to show that there is some disposable income available to make monthly payments. “If you’re very deep under water and not even close to making the payment work, they’re less likely to help you,” Firoved says. “It’s a little ironic, but you need to be able to afford the adjustment that is being made to [the existing] loan that you can’t afford.”

The Homeowner’s Toolbox costs $99—but it comes with a money-back guarantee if your application gets turned down. Firoved says that, down the line, he would like to give the product away for free. But for now, he adds, “we’re keeping the cost minimal.”

An addendum to today’s post: the Center for Responsible Lending has just issued a report noting that, in the first three months of 2009, seven times as many home loans were on the brink of foreclosure than were modified.