The open floor of a basement, framed through to flooring, prices at about $30 to $50 a square foot in 2026 (Angi, most projects; $30 to $75 across the full range). On 900 square feet that is $27,000 to $45,000. Everything that makes a basement harder than a room upstairs sits outside that rate and goes on its own line: an egress window at $2,723 to $5,898 installed (HomeAdvisor, June 2026), a bathroom rough-in at $3,000 to $20,000 (Angi), a sewage ejector pump at $850 to $3,500, radon mitigation at $800 to $2,500, and whatever the ceiling height forces. The average remodeler nets 6.3% (NAHB), which is $2,016 on a $32,000 basement. One egress window absorbed into the per-foot rate is twice that.
What should you charge per square foot to finish a basement?
Quote the open floor by the foot. Nothing else. The published ranges disagree by a factor of ten, and the disagreement is about what is inside the number.
| Source | Per sq ft | What it covers |
|---|---|---|
| HomeAdvisor, June 2026 | $7 to $23 | "Basic finishing," the homeowner's starting expectation |
| Fixr, 900 sq ft finish | $17 to $33 | $15,000 to $30,000 total, open plan, no bath |
| Angi, 2026 | $30 to $50 | Most contractor-led projects; $30 to $75 full range |
| Fixr, full remodel | $30 to $90 | Bathroom, bedroom, kitchenette or theater |
Your number lives in the Angi row. HomeAdvisor's $7 to $23 is the figure the homeowner read before you arrived, so know where the gap goes. HomeAdvisor's own element prices explain most of it: framing $7 to $16 per square foot, insulation $0.30 to $6.75, a finished ceiling $9 to $13, permits $1,200 to $2,000. Those four pass $23 before an outlet goes in.
Then stop using the foot. A 600 square foot basement with a bathroom and an egress window can cost the same as 1,200 square feet with neither, and only the lines below can tell them apart.
What does an egress window add to a basement estimate?
Price it as its own job, with its own permit, at $2,723 to $5,898 installed per HomeAdvisor's June 2026 guide, average $4,244. Excavation is $1,500 to $3,000 of that, the well $500 to $1,000, and HomeAdvisor budgets three days or more of labor at $40 to $100 an hour. A lintel adds a structural engineer at $200 to $1,500.
The homeowner has a different number. HomeAdvisor's basement finishing page lists egress windows at $200 to $950, the window and the labor to set it, with the digging and the cut left out. The gap between the two pages is the hole.
| 2021 IRC R310 requirement | Figure |
|---|---|
| Net clear opening | 5.7 sq ft (5 sq ft at grade floor) |
| Minimum clear height | 24 in |
| Minimum clear width | 20 in |
| Maximum sill height above floor | 44 in |
| Window well area | 9 sq ft, 36 in projection |
| Ladder or steps | Required when the well is deeper than 44 in |
Source for the table: Boulder County's B10 handout. Read the first line of R310.1 before a homeowner talks you out of the window. Basements with habitable space need an emergency escape opening. Not bedrooms only. The "office" that will be a bedroom on the listing in five years needs one, and so does the office that stays an office. Skip it and the inspector adds it back at your expense, after the drywall is up.
The low end is real, for the right house. One mason in a Fine Homebuilding thread charged $650 to cut an 8-inch poured wall, set the window and dig and ring the well. That is soft dirt and nothing buried. A well 5 feet deep beside a gas line is the other end of HomeAdvisor's range, and you only learn which you have by walking the outside of the house.
How do you price a basement bathroom rough-in?
Find the sewer exit before you write a number. Angi's 2026 range for bathroom rough-in plumbing is $3,000 to $20,000, average $6,500, and a basement bath lives in the top half of it because the drain lines go under a slab that has to be cut and patched. The question that decides the price is where the main leaves the house. Below the slab, gravity drains and the rough-in is a plumber for two or three days at $80 to $130 an hour plus the concrete work. Above the slab, which is common in older houses on septic or a shallow sewer, every fixture drains to a pit and a sewage ejector pump lifts it. HomeAdvisor's June 2026 figure for the pump installed is $850 to $3,500, average $2,300.
So the bathroom carries three lines before a tile is set: the slab cut and patch, the rough-in, then the pump if the exit says so. Then the finish, which prices like any other bath. Fixr puts a full basement bathroom addition at $20,000 to $30,000, and the bathroom remodel estimate you already know how to build handles the room once the drains are in. Keep the pump as its own line even when you are sure of it. An upflush macerating toilet avoids the slab cut, and the line is what lets the homeowner see that choice.
What do moisture and radon cost before you hang drywall?
Test, then quote. Both are cheap before the walls close and expensive after. The EPA's action level for radon is 4 pCi/L. Its Consumer's Guide to Radon Reduction says most homes are fixed for about the cost of other common repairs, and the EPA's published range for retrofitting a system is $800 to $2,500, average about $1,200 (EPA archive). Colorado and Utah, where Google Trends shows the most interest in finishing basements, are both high-radon states.
Write the test as a line and the system as an allowance. A sub-slab suction pipe set before framing is a core drill and a fan. The same pipe after drywall means a finished wall opened and refinished. The EPA is also direct that sealing cracks on its own is not an accepted fix, so a homeowner who wants to "just caulk it" is asking you to sign off on something the agency will not.
Moisture is the same shape. HomeAdvisor puts basement waterproofing at $4,400 and a sump pump at $575. Fixr prices mold removal at $1,500 to $4,000. None of it is in the per-foot rate. Tape a square of plastic to the block wall on the first visit and look at it on the second. Condensation under the plastic is one problem and water on the outside of it is another, and with the efflorescence line along the wall they tell you whether this is a finish job or a drainage job with a finish at the end. Say which one it is in writing, next to your other written exclusions.
How do you price framing basement walls off concrete?
Hold the wall 1.5 inches off the concrete, put 2 inches of rigid foam against the wall first and seal it, and set a pressure-treated plate on a sill seal with coated pins. That is the method the carpenters in a Fine Homebuilding thread settled on, and it is why basement framing prices above upstairs framing. HomeAdvisor's $7 to $16 per square foot covers the extra stud wall, the plumb line that ignores the foundation, and the time spent on a wall that bows an inch across 20 feet.
The line that gets missed is fireblocking. The gap you just built is a concealed draft opening, and IRC R302.11 wants it blocked at the ceiling line and the floor, with the same at 10-foot intervals in a furred wall (Bridgewater, Connecticut guide). A framer on the thread put it bluntly: without it you are building a fire hazard. Inspectors look for it. Price the material and an hour per 40 feet of wall. Or price the return trip.
When does ceiling height change the whole estimate?
Measure under the duct, not in the open. IRC R305.1 requires 7 feet over habitable space, 6 feet 8 inches in bathrooms and laundry rooms, and lets beams and ducts project down to 6 feet 4 inches. A basement with 7 feet 2 inches to the joists and a 10-inch trunk line where the family room goes is not a 7-foot room under the trunk. It is a soffit or a rerouted duct, and both are lines.
When the slab itself is too low, the job changes kind. Fixr prices lowering a basement floor at $31,500 to $63,000 and leveling one at $1,200 to $15,000. At that point you are underpinning, not finishing, and the estimate needs an engineer before it needs you. Say so and walk away.
When do homeowners look for a basement contractor?
January through April. Google Trends for "finish basement cost" in the US over the 12 months to October 4, 2026 peaks the week of March 1 at 100 and falls to 37 in the week of September 20. If you advertise basement work, spend in December and January when the searches start, not in June when your schedule opens up. The rising queries are "cost to finish a basement per square foot" at +90% and "how to finish basement walls" at +80%.
What this misses
The per-foot range is national and wide. Angi's $30 to $50 is a sanity check on your own number, not a replacement for it. A Denver basement and a Birmingham basement do not share a rate.
Code is local. The IRC figures above are the model code. Connecticut, for one, allows 6 feet 8 inches in existing basements converted to habitable space. Read your jurisdiction's handout before you quote headroom.
Egress and plumbing prices move with the dirt. A gas line, a buried downspout drain or a high water table turns a $650 cut into a $5,000 one, and no table shows that.
Set your contingency from the things on this list you could not verify on the walk. The hard part is that the sewer exit, the duct height and the radon test all have to be found while you are standing on the slab with a flashlight, and the estimate gets written somewhere else. BidWalk captures the egress, the pump and the fireblocking as you walk the basement and say them, so the lines that eat the margin are on the page before you climb the stairs.
