The average homeowner doesn't have to take many steps past the front door before 'the list' grows. Whether the latest to-do entry is small, such as replacing a ripped window shade, or a grand dream of a master bath suite, two things are certain in the land of homeownership: There's always something else to be done, and it'll cost you.

With more involved projects in mind -- and perhaps backed up by piggybank-busting estimates -- you may start to wonder if it will all be worth it in the end.

Considering your home's worth is one way of attacking the equation. On average, don't put more than 20 percent of a home's value into improvements on the home, most industry experts say.

"I've always been hesitant to endorse averages because every house has its own story," says Gregg Hicks, director of marketing for Reliableremodeler.com.

From the age and condition of the home to what the Joneses of the neighborhood have done, there are a lot of factors to help in deciding how much work may be necessary and, likewise, what would be considered going overboard.

In 2005, Dan Fritschen, author of "Remodel or Move?" and founder of a Web site by the same name, surveyed 5,000 homeowners who felt underserved by their current living quarters and found that one-third of those who intend to remodel will spend 30 percent of their home's value on the project.

One of custom home builder Bob McLemore's current projects is providing $285,000 in additions and remodeling to a home valued at $200,000 before the project began. Located in a rural area, the house has appreciated nicely, says McLemore, founder of the Charlotte, N.C.-based firm HouseRaising.

Better or bust
So what does it take to get a thumbs-up on improvement spending from the experts? Neighborhood knowledge. Consider the highest priced home as a limit.

"You can improve up to that level," says Fritschen. "Going over that is strictly quality of life." In other words, you'd better enjoy that fourth bathroom and natural stone-surrounded pool with waterfall if nearby houses have no such amenities.

Or, as Becky Nelson, senior loan officer for Opteum Financial Services puts it, if you want $50,000 in custom landscaping while your immediate neighbors are struggling to mow their lawn, that's fine. But when you move, you're not getting the $50,000 back.

That is especially important to remember with tract-type neighborhoods, McLemore says. A house that's not "normal," even in a good way, won't rebound from the costs of improvement. On the other hand, a home in an older, in-demand neighborhood is more likely to grow in comparable value as improvements are made.

As for the work-with-what-you've-got-or-build-an-addition decision, consider a calculation from Dean Bennett, president of a Colorado-based design and construction firm, who says adding square footage often makes good sense: Divide the total cost of the addition by the number of square feet added and then compare that number to the cost per square foot of what homes in the area are selling for. For example, a $75,000 addition of 400 square feet would cost $187.50 per square foot. Compare that figure to the cost of a square foot in comparable houses in the neighborhood.

Still, Bennett says, "Determining if home improvement projects are worth it is more often about making things more livable for the homeowner."