Why construction loans are more complex than purchase mortgages
A purchase mortgage is simple: you borrow a fixed amount to buy an existing house at a fixed rate. A construction loan is structurally different. You’re borrowing against a building that doesn’t exist yet, with disbursements happening in stages as work is completed, at a variable rate tied to prime, and ultimately converting to a permanent mortgage once the building is done. Each of these differences adds cost and complexity that most first-time custom-home builders underestimate.
A typical custom build in 2026: $90,000 land + $340,000 contractor bid = $430,000 before contingency. Add 10% contingency ($34,000) and the project is $464,000. Add 9 months of construction at 8.5% interest on average $186,000 outstanding = $11,800 interest during build. Add 2% origination + closing fees on the construction loan = $9,300. Add $2,500 for permits, utilities hookup, and site surveys. Total real cost: ~$487,600 — about 13% above the contractor bid.
And that’s if everything goes well. The typical custom build runs 15-25% over budget for various reasons: weather delays, material price spikes, change orders, permit issues, contractor disputes. Budget 20% overrun contingency to be safe.
Construction loan types
Construction-to-permanent (C2P): Single loan, single closing. Acts as a construction loan during the build, then automatically converts to a permanent mortgage after occupancy. Advantages: one closing cost ($3-8K), one appraisal, simpler. Disadvantages: you’re locked into the permanent rate set at closing — if rates drop during construction, you can’t get the benefit without float-down options.
Stand-alone construction + separate permanent loan: Two separate loans, two closings. First loan covers construction only; you refinance into a permanent mortgage after the house is done. Advantages: can shop rates twice, may save if rates drop. Disadvantages: double closing costs ($6-15K combined), double stress, risk of being unable to qualify for the permanent loan if your financial situation changes during build.
Owner-builder loans: For those acting as their own general contractor. Rare and restrictive — most lenders require licensed GCs. If allowed, rates are higher (0.5-1.5% premium) and reserves required.
Renovation loans (FHA 203k, HomeStyle): Different animal — for buying and renovating an existing home, not building new. Covers up to $75K (limited 203k) or actual project cost (standard).
How construction interest actually works
Construction loans don’t disburse the full amount upfront. Instead, funds are released in “draws” as milestones are completed: foundation (20%), framing (20%), roof + windows (20%), mechanical rough-in (15%), drywall + flooring (15%), final completion (10%). Interest is only charged on the amount disbursed, not the full loan.
This is why construction interest is typically lower than you’d expect. On a $372,000 construction loan (after $92,000 down), during a 9-month build, your average outstanding balance is roughly half the final total ($186,000). At 8.5% construction rate, that’s $13,185 in total construction interest — not the $28,000 you’d calculate by naively applying 8.5% × $372K × 0.75 years.
Payment structure during construction is typically interest-only. You pay roughly $1,500-$2,000/month at peak construction (when balance is highest). Then when the house is complete and the loan converts to permanent, you start paying principal + interest on the final balance.
Contingency: the variable that separates successful builds from disasters
Most contractors will quote you a “firm price” for the build. In reality, 80%+ of builds go over by 5-20%, often from causes that weren’t anyone’s fault at bid time.
Material price changes: Lumber, steel, copper can swing 30%+ in a single year. Most contractors lock in materials at bid but not for long periods.
Soil conditions: Foundation work can hit rock, water, or poor soil that requires expensive engineering solutions.
Permit and inspection issues: Code changes, permit delays, failed inspections requiring rework.
Change orders: You decide mid-build you want upgraded countertops, different windows, extra outlets. Each change adds 15-30% premium vs if it had been in the original spec.
Weather delays: A rain-heavy spring can add weeks to foundation and framing. Labor costs don’t pause for weather.
Budget 10-15% contingency in your loan to handle these. If you don’t use it, great — you pay less interest. If you need it, you’re not scrambling for a HELOC mid-build.
Qualification is tougher than purchase mortgage
Down payment: 20-25% minimum typical (vs 5-10% for conforming purchase). Some lenders will accept land as part of down payment if you already own it.
Credit score: 700+ typical minimum (vs 620 for conforming purchase). Best rates at 740+.
DTI: 43% max usually, including the proposed permanent mortgage payment.
Reserves: 6-12 months of PITI in savings post-closing. Much higher than purchase loan requirements (0-2 months typical).
Detailed plans and budget: Architectural plans, contractor bids, line-item budget, specifications. Lender will review for reasonableness.
Licensed builder: GC must be licensed, insured, bonded. Owner-builder loans are very restrictive if allowed at all.
The financial commitment most builders underestimate
Beyond the loan itself, you’re committing to serious ongoing cash flow during the build.
Rent during construction: 9-12 months of paying rent somewhere while the house is built. $18,000-$36,000 depending on your area.
Construction interest payments: $1,000-$2,500/month peak payments during build.
Unexpected out-of-pocket costs: Small items not covered by contractor (appliance upgrades, landscaping, window treatments). Budget $15,000-$30,000 beyond the loan.
Moving costs: $3,000-$8,000 typical.
New furniture/decor: Most new-build owners spend $15,000-$50,000 outfitting. It’s a bigger house than their old place.
Total out-of-pocket on top of the construction loan: often $50,000-$100,000. Plan accordingly.
Related calculators
- Mortgage payment — permanent loan payment detail.
- LTV — permanent loan LTV.
- Closing costs — additional closing if split loans.
- Affordability — max build you can afford.