Doing home-improvement jobs yourself can be a smart way to save money, but choose the right DIY projects or you’ll end up paying dearly.

Look for maintenance jobs that are relatively easy and need to be done regularly, so you can hone your skills over time.

Why pay someone big bucks to do something you can just as easily do yourself? That’s the thinking that has gotten more Americans than ever swinging their own hammers. In a recent Time magazine poll, nearly a quarter of people said they were taking on more home-improvement projects themselves—understandably so, when you consider that it usually means a 50% to 75% discount, since all you pay for is materials.

But sometimes doing it yourself costs more than it saves, like when you decide to replace the toilet, end up flooding the basement, and have to pay a pro to fix your mistakes. Or, worse, if you become one of the more than 100,000 people injured each year doing home-improvement jobs. Here are some guidelines for deciding when DIY can save you money and when it could cost you. 

Stick to routine maintenance for savings and safety

Seasonal home maintenance is ideal work for the DIY weekend warrior, since you can plan tasks in advance and get to them when your schedule allows. Because these are repeat projects, your savings will add up to big bucks over the years. Just by mowing your own lawn, for example, you can save $55 to $65 a week for a half-acre lawn during the growing season. The bigger the lot, the bigger the savings: with two acres, you’ll pocket around $150 per week. 

When It Pays: Look for maintenance jobs that are relatively easy and need to be done regularly, so you can hone your skills over time. In addition to mowing, other good ones are snow removal, pruning shrubs, washing windows, sealing the deck, painting fences, fertilizing the lawn, and replacing air conditioner filters. 

When It Doesn’t: Unless you have skill and experience on your side, stay off of any ladder taller than six feet; according to the U.S. Consumer Product Safety Commission, more than 164,000 people end up in emergency rooms every year because of ladder injuries. The same goes for operating power saws or attempting any major electrical work—it’s simply too risky if you don’t have the experience.

Act as your own GC on small jobs 

If you’re more comfortable operating an iPhone than a circular saw, you may be able to act as your own general contractor on a home-improvement project and hire the carpenters, plumbers, and other tradesmen yourself. You’ll save 10% to 20% of the job cost, which is the contractor’s typical fee. 

When it Pays: If it’s a small job that requires only two or three different tradesmen, and you have good existing relationships with top-quality professionals in those fields, consider DIY contracting.

When It Doesn’t: Unless you have an established network of contacts who will show up as promised, the time to spend on oversight, enough construction experience to spot potential problems, and the skill to negotiate disputes between the various subcontractors, trying to manage your own project can quickly send the schedule and budget off the rails.

Pitch in with sweat equity on big jobs

Contributing your own labor on a big job being handled by a professional crew can cut hundreds or even thousands of dollars off the contractor’s bill. Tear the cabinets and appliances out of your old kitchen before the contractor gets started, say, and you might knock $800 off the cost of your remodel, says Dean Bennett, a design/build contractor in Castle Rock, Colorado.

 When it Pays: Grunt work—jobs that are labor intensive but require relatively little skill—makes the best homeowner contribution. Offer to do minor interior demolition like removing cabinets and pulling up old flooring, daily jobsite cleanup, product assembly, and simple landscaping like planting foundation shrubs and grass seed around your new addition.

 When It Doesn’t: If you get in the crew’s way, you may slow them down far more than you help. Make your contributions when the workers aren’t around, such as in the morning before they arrive, or on nights and weekends after they’ve left.

Put on some of the finishing touches

Unlike the early phases of a construction job, which require skilled labor to frame walls, install plumbing pipes, and run wiring, many of the finishing touches on a project are comparatively simple and DIY-friendly. If you do the painting yourself for a new basement rec room, for instance, you can easily save $1,800, Bennett says. 

When it Pays: If you have the skill—or a patient temperament and an experienced friend to teach you—finish work like setting tile, laying flooring, painting walls, and installing trim are all good DIY jobs.

 When It Doesn’t: The downside to attempting your own finish work is that the results are very visible. Hammer dents in woodwork, for example, or sander ruts in your hardwood floors may cause you aggravation every time you see them. So unless you have a sure eye and a steady hand, it may not pay to embark on these tasks.

A former carpenter and newspaper reporter, Oliver Marks has been writing about home improvements for 16 years. He’s currently restoring his second fixer-upper with a mix of big hired projects and small do-it-himself jobs.