Construction Loan Calculator

Understanding Construction Loans

Building a new home or undertaking a major renovation requires specialized financing that differs significantly from a traditional mortgage. Construction loans are designed to fund the building process, with unique payment structures and requirements that borrowers need to understand before committing. Our construction loan calculator helps you estimate the permanent mortgage payment you will face once building is complete.

What Is a Construction Loan?

A construction loan is a short-term financing product used to fund the building of a new home or major renovation project. Unlike a standard mortgage where you receive the full loan amount upfront, construction loans are disbursed in stages called draws. Each draw corresponds to a completed phase of construction, such as foundation, framing, roofing, and finishing. The lender typically sends an inspector to verify that each phase is complete before releasing the next draw. This staged approach protects both the lender and the borrower by ensuring funds are used for their intended purpose.

How Construction Loans Differ from Traditional Mortgages

Construction loans differ from traditional mortgages in several key ways. First, they are typically shorter in duration, lasting only the construction period plus a short window for completion. Second, interest rates on construction loans are higher than conventional mortgage rates because the lender assumes more risk: there is no completed property to serve as collateral. Third, the qualification process is more stringent, often requiring detailed building plans, a construction budget, a licensed contractor, and sometimes an appraisal of the planned home. Finally, rather than receiving a lump sum, funds are released incrementally as construction progresses through the draw schedule.

Interest-Only During the Construction Phase

One feature that makes construction loans more manageable is the interest-only payment structure during the build phase. Instead of making full principal and interest payments from day one, borrowers pay only the interest on the amount that has been drawn so far. For example, if your total construction loan is $350,000 but only $100,000 has been drawn after the first month, your interest-only payment is based on $100,000, not the full loan amount. As more draws are released, the interest-only payment increases gradually. This structure keeps payments lower during construction when you may also be paying for temporary housing or your current mortgage. Use our construction loan calculator above to estimate what your full payment will be once the loan converts to permanent financing.

Converting to a Permanent Mortgage

Once construction is complete, the loan transitions to the permanent phase. There are two main types of construction loans. A construction-to-permanent loan (also called a single-close or one-time-close loan) automatically converts to a standard mortgage after construction, locking in your permanent rate upfront. This eliminates the need for a second closing and additional closing costs. A stand-alone construction loan must be paid off or refinanced into a separate mortgage once building is finished, requiring two separate loan applications and closings. Construction-to-permanent loans are generally preferred because they offer rate certainty and cost savings, though stand-alone loans may provide more flexibility in shopping for the best permanent mortgage rate after construction.

Construction-to-Permanent Loans (Single-Close)

A construction-to-permanent loan — often abbreviated "construction to perm" or "CTP" — wraps the construction phase and the permanent mortgage into a single loan with one closing. You qualify once, sign once, pay one set of closing costs, and the interest rate on the permanent phase is locked before construction begins. Construction-to-permanent loans are the dominant product at most national and regional lenders for owner-occupied new builds, including FHA, VA, and conventional versions. The VA construction-to-perm program (single-close) is one of the few ways to finance a custom build with 0% down. Fannie Mae and Freddie Mac both publish construction-to-permanent guidelines for conventional single-close loans.

How the construction to perm calculator models this: You enter a construction rate (typically prime + 1% – 2%, currently 8% – 10%) and a permanent rate (currently 6% – 7% for a 30-year fixed). the construction loan calculator runs two phases: interest-only payments on drawn balances during the build (typically 6 – 12 months), then full amortization on the total loan amount for 15 – 30 years after the conversion. This matches the disclosure structure on a single-close Loan Estimate.

Construction-to-Permanent vs Stand-Alone (Two-Close)

Interest-Only Construction Phase Math

During the construction phase, payments are interest-only on the drawn balance, not the total loan amount. If your construction loan is $400,000 but only $100,000 has been drawn to the foundation contractor in month 1, your interest-only payment is on $100,000. At a 9% construction rate, that's $100,000 × 0.09 / 12 = $750/month in month 1. By month 6, with $300,000 drawn, payment climbs to $2,250/month. The construction loan calculator above models this phase correctly — most competing calculators skip it and quote you the full permanent payment from day one, which under-states your real monthly cost during construction.

Building with Land Equity

If you already own the lot free and clear, your land equity can count toward your down payment on a construction-to-permanent loan. Lenders typically appraise the "as-completed" value of the property and require the borrower to have at least 5% – 10% equity in the combined land-plus-improvements. For example: if your lot is worth $100,000 and the build cost is $400,000, total project cost is $500,000. A lender requiring 10% down wants you to have $50,000 in equity — your lot's $100,000 value already covers this. You can finance the entire $400,000 build with no additional cash. the construction loan calculator above lets you see what payments look like on this combined structure.

Tips for Managing Construction Loan Costs

Managing a construction loan effectively starts with careful planning. Build a contingency budget of 10 to 20 percent above your estimated construction costs, as overruns are common. Choose an experienced, licensed contractor with a solid track record, as lender requirements for contractor credentials can affect loan approval. Lock in your permanent mortgage rate early if using a construction-to-permanent loan to protect against rate increases during the build. Make sure your construction timeline is realistic, as extensions can be costly and some loans impose penalties for delays. Finally, consider making extra payments toward principal once the loan converts to permanent financing to reduce total interest costs over the life of the loan. Explore our DSCR calculator for investment property construction, or the home equity calculator if you are using equity to fund your build.

Worked Example: $350,000 Build at 8% Construction / 6.5% Permanent Over 30 Years

This walkthrough uses the construction loan calculator's default inputs. Construction loans have two distinct payment phases with different math for each.

Step 1 — Construction phase (interest-only on drawn amounts)

During the 12-month build, you pay interest only on funds actually drawn. The peak payment occurs when the full $350,000 is drawn:

Peak monthly interest = $350,000 × 0.08 ÷ 12 = $2,333.33

In practice, draws are incremental (foundation, framing, drywall, finish), so the average outstanding balance is roughly half. Typical total construction-phase interest on a 12-month build runs about $14,000 ($350,000 × 8% × 0.5 average draw × 1 year, simplified).

Step 2 — Permanent phase (standard amortization)

Once the build completes, the loan converts to a 30-year amortizing mortgage at 6.5%. The full $350,000 principal (plus any rolled-in construction interest) is now amortized:

r = 0.065 ÷ 12 = 0.005417 (1.005417)^360 ≈ 6.991 M = 350,000 × [0.005417 × 6.991] / [6.991 − 1] M ≈ $2,212.24 / month

Step 3 — Total cost of the loan

Permanent phase: 360 payments of $2,212.24 = $796,406 total. Subtracting the $350,000 principal leaves $446,406 in permanent-phase interest over 30 years. Add the ~$14,000 construction-phase interest for a combined interest cost of roughly $460,000.

Step 4 — Verify in Excel or Google Sheets

=350000*0.08/12 → $2,333.33 (peak construction interest) =PMT(0.065/12, 360, -350000) → $2,212.24 (permanent payment)

Assumptions & limitations

• Construction-phase interest is modeled at the peak draw amount. Real draws are staged (typically 5–6 inspections), so actual interest accrual is lower early in the build.
• Construction-to-permanent (single-close) structure assumed. Stand-alone construction loans require a separate refinance, with new closing costs and rate risk at conversion.
• Permanent rate is locked upfront in this model. Some loans float the permanent rate during construction, exposing the borrower to rate risk.
• Contingency reserves (typically 10–20% of project cost) are not modeled. Most lenders require them; underused contingencies may reduce principal at conversion.
• Loan-to-cost (LTC) ratio caps are not enforced here. Most construction lenders cap LTC at 75–85% of total project cost (land + hard costs + soft costs).

Sources & Editorial Standards

Construction loans combine two distinct formulas: simple interest during the build phase, then standard amortization M = P × [r(1+r)^n] / [(1+r)^n − 1] after conversion. Our calculator exposes both phases rather than collapsing them into a single number, which would hide the interest-only draw mechanics that define this loan type.

Primary sources for construction loan standards and market data:

• National Association of Home Builders (NAHB) — construction cost benchmarks and draw schedule conventions used by U.S. builders and lenders.
• Fannie Mae HomeStyle® Renovation & Construction — conforming construction-to-permanent program guidelines that benchmark lender LTC and draw inspection requirements.
• HUD — FHA 203(k) Rehabilitation Mortgage — government-backed construction/rehab loan structure with standardized draw and inspection rules.
• Construction Financial Management Association (CFMA) — industry benchmarks for construction project cost overruns that inform contingency reserve sizing.

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