Free Deck Cost Calculator (+ Guide)

What is a deck cost calculator?

A deck cost calculator adds up every cost of building a deck, from the deck builder's quote to the lighting you add yourself.

It shows the total with a contingency, the cost per square foot and what's left of your budget.

How it works

The cheapest of your quotes goes in the total, next to the costs it doesn't cover.

What the building code asks of a deck

The 2024 International Residential Code, the model code most US towns adopt in some form, has a section on wood decks.

• Footings: at least 12 inches below undisturbed ground, and below the frost line when the deck is attached to a house with frost-protected footings (R507.3.2, R507.3.3)
• Ledger: the board bolted to the house is at least a 2x8, and never hangs on stone or masonry veneer (R507.9.1.1)
• Guards: needed wherever the deck is more than 30 inches above the ground within 36 inches of the edge, at least 36 inches high, with no gap a 4-inch ball can pass (R321.1)
• Small low decks: a free-standing deck of up to 200 sq ft, no more than 20 inches up, can sit on precast pier blocks with no footings (R507.3)

Your town may use another edition or its own changes, so ask its building department what applies.

Call 811 before the footings

The US Department of Transportation asks everyone to call 811 a few days before any digging, building a deck included.

The call connects you to local utility operators, who mark the approximate location of buried gas, electric, telecommunications, water and sewer lines. It's been the national number since 2005.

How to compare contractors' quotes

The Federal Trade Commission gives this advice before you hire anyone.

• Hire only licensed and insured contractors, and check the license with your state or county
• Get several written estimates, each with the work, the materials, the completion date and the price
• Don't automatically pick the lowest bid, and ask why if the estimates differ a lot
• Get a written contract with the contractor's license number and the start and finish dates
• Never pay the full amount up front, and make the final payment only when the work is done

It also warns that a contractor who asks you to get the permits, or who only takes cash, may be running a scam.

How much contingency to add

A contingency is money set aside for what you find once the walls or the ground are open.

HUD requires one on its 203(k) renovation loans: 10% to 20% of the repair costs on a home 30 years or older, and at least 15% when the utilities don't work.

On a newer home, it's up to the lender, to a maximum of 20%.

A worked example

Here's the example the calculator loads: a 300 sq ft deck with three quotes of $14,000, $16,500 and $12,800, plus permits, a stain and lighting you're buying yourself.

The cheapest of the three quotes is $12,800, $3,700 less than the dearest. Your other costs add $1,400, so the deck comes to $14,200 before the contingency.

A 10% contingency adds $1,420, for a total of $15,620. That's $52.07 per square foot, and $4,380 left of a $20,000 budget.

Mistakes to avoid

These are the slips that come up most.

• Comparing quotes that use different decking, railings or footing depths
• Leaving the guard out of the budget on a deck more than 30 inches up
• Digging footings without calling 811 a few days ahead

Who is the deck cost calculator for?

It's for anyone planning a deck, from a low platform to a raised deck off the kitchen, and these tools help around it.

• Concrete calculator – for the footings
• Square footage calculator – for the deck's area
• Home equity loan calculator – if you borrow for it

Price the parts that hold it up before the boards you'll see, and the deck lasts as long as it looks good.