It’s one of the unwritten rules of remodeling that a project will always cost more and take longer than expected. But just because this is the norm, you don’t have to take it as a given. With the right combination of planning, discipline and smart shopping, your renovation can end on budget and ahead of schedule. Here’s how to get there:

Build a cushion. Hidden surprises, including structural damage behind walls and outdated electrical, are the biggest remodeling budget busters. Building a 10 to 15 percent cushion into your initial budget will help cover these unforeseens.

Involving your contractor early in the process also helps set a realistic budget. While they can’t see through walls, they might be able to do a pre-inspection of the house to spot potential problem areas. A spongy bathroom floor, for example, is a sure sign of water damage.

Getting your contractor on board early will also stop you from falling in love with a design that’s way beyond your budget.

Negotiate upfront. Most contractors are willing to haggle over the price of the job. That’s especially true if they know you’ll turn into a repeat customer, so if you have additional projects in mind, be sure to share that information upfront.

Getting bids from multiple contractors will increase your bargaining power. You should also check HomeAdvisor’s True Cost Guide to get a handle on the current market rate for a given project. As with any deal-making, the more information you have, the stronger your position will be.

Stick to the plan. It’s often said that the four most expensive words in home remodeling are “while we’re at it.” If you’re intent on sticking to the budget, you must resist the urge to change the design plan after the work is underway.

The more detailed the design, the easier this will be. Avoid a lot of “allowances” in the written contract, basically blank spaces that your contractor will fill out later, say for light fixtures or flooring materials. It’s easy to underestimate how much these items will cost.

Do some of the work yourself. DIY can help control project costs. Just be sure to make it part of the initial negotiations with your contractor. Low-impact prep work is ideal, say tearing up carpets or taking away old cabinets.

Unless you’re an experienced DIYer, think twice about taking a sledgehammer to walls. The work is messy and backbreaking, plus you run the risk of damaging load-bearing walls or buried plumbing and electrical lines.

At the back end of the project, finish painting is a great project to tackle yourself. Doing so could shave a few percentage points off the total budget.

Go bargain hunting. Salvage yards and second-hand stores can be great sources for inexpensive remodeling wares, from fireplace surrounds to bathroom vanities. There are even retailers that sell entire kitchen sets (cabinets, countertops, appliances and more) that have been carefully removed from high-end residences.

On a major project, like a gut kitchen renovation, the measure could save you tens of thousands of dollars. But making used materials fit your space will present design and installation challenges, so it’s important to work with an architect and contractor with the right skill set and experience.

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Dan DiClerico is a home expert for HomeAdvisor, an online marketplace connecting homeowners with trusted service professionals to complete home projects. Visit HomeAdvisor.com