Construction Loan Calculator
Model a construction loan where funds are drawn in stages, interest accrues only on what has been advanced, and the balance converts to a permanent mortgage on completion.
Construction Loan Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Results are a model, not a quotation — an institution's own figures govern.
- Every input is an assumption; change one and the answer changes with it.
- Rounding is applied only at the display layer, so totals may differ by a cent from a statement that rounds each line.
In short: Construction loans charge interest only on drawn funds, so cost depends on the draw schedule. A $400,000 build over twelve months at 7.5% with even draws accrues $16,250.00 of interest — the payment rising from $208.33 in month one to $2,500.00 in month twelve.
Formula
Because the balance climbs from one draw to the full amount, average exposure is a little over half the build cost, not the whole of it.
Worked Example
- Set the draw. $400,000 over 12 months = $33,333.33 per month.
- Month one. Interest on $33,333.33 at 7.5% = $208.33.
- Month twelve. Interest on the full $400,000 = $2,500.00.
- Total it. The rising series sums to $16,250.00.
- Convert. The permanent loan at 6.5% over 360 months costs $2,528.27.
Analyst note. Interest of $16,250.00 is far below the $30,000.00 the full balance would accrue, because average exposure is only $216,666.67. Budget for the payment escalating twelvefold across the build — borrowers who plan around the first month's $208.33 are routinely caught out by month twelve. Most lenders permit interest reserves to be capitalised, which smooths cash flow but adds to the balance.
Strengths & Limits Of This Model
Where this engine is strong
- Runs entirely in your browser — no figure you type is transmitted or stored.
- Shows the full working, so every number can be traced and challenged.
- Free, unmetered and free of affiliate incentives.
Where it stops
- Generalised assumptions cannot capture every individual circumstance.
- Jurisdiction-specific rules and mid-year changes may not be reflected.
- A model output is not a substitute for a professional review of your position.
Practical Use Cases
Budgeting cash flow through a build
The payment rises every month as draws accumulate. Knowing the final month figure in advance is the difference between a managed build and a cash crisis. Check the permanent payment with the Mortgage Payment Calculator.
Comparing construction-to-permanent against two closings
A single-close loan converts automatically and avoids a second set of fees. Price that saving with the Closing Cost Calculator.
Modelling a delayed build
Extend the build period and the interest cost rises with it. Overruns are common, so run eighteen months as well as twelve, and check the land component with the Land Loan Calculator.
Methodology & Editorial Standards
Draws are assumed even across the build period, which is the standard planning assumption though real schedules are lumpier, weighted toward foundation and framing early and finishing trades late. Interest is charged monthly on the cumulative amount advanced, not the approved facility, which is the defining feature of construction lending. The average balance follows the arithmetic series and is slightly above half the total cost. The permanent payment amortises the full build cost at the permanent rate over the chosen term, reflecting a single-close construction-to-permanent structure. Land cost, contingency reserves and capitalised interest reserves are excluded; lenders typically require a contingency of five to ten percent above the contract price. The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Construction Loan Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How does interest work on a construction loan?
It accrues only on funds drawn, not the approved amount. With even draws on a $400,000 build, month one costs $208.33 and month twelve costs $2,500.00, totalling $16,250.00.
What is a draw schedule?
The staged release of funds as work completes, typically at foundation, framing, mechanicals, drywall and completion. Each draw is usually inspected before release.
Why is my payment so small at first?
Because almost nothing has been advanced. The payment scales with cumulative draws, so it rises throughout the build — twelvefold in this example, which must be budgeted for.
What is construction-to-permanent financing?
A single loan that converts to a standard mortgage on completion, avoiding a second closing and second set of fees. The alternative is a standalone construction loan refinanced at the end.
How much deposit do I need to build?
Typically 20% to 25% of total project cost, and lenders usually credit land you already own toward it. Requirements are stricter than for purchase mortgages because the collateral does not yet exist.
What happens if the build runs over budget?
You cover it, usually in cash, since the loan is sized to the approved budget. Lenders require a contingency of five to ten percent for this reason, and it is prudent to hold more.
Can I capitalise the interest?
Many lenders permit an interest reserve funded from the loan, so no cash payments are made during the build. It smooths cash flow but increases the balance and the eventual permanent payment.
Are construction rates higher than mortgage rates?
Usually by one to two points, reflecting the risk of lending against an incomplete structure. They are also frequently variable, tied to prime, which adds exposure during a long build.
What if the build takes longer than planned?
Interest accrues for longer and extensions may carry fees. Overruns are common, so model eighteen months as well as twelve before deciding the budget is adequate.
Do I need a licensed builder?
Almost always. Owner-builder loans exist but are far harder to obtain and require demonstrated construction experience. Lenders want a fixed-price contract with a bonded contractor.
How is the appraisal done on a build?
Against the completed plans and specifications, producing an as-completed value. If that value comes in below cost, you must fund the difference — a real risk on highly customised builds.
Is renovation financed the same way?
Similar in structure, using staged draws against completed work, but renovation loans are usually smaller and shorter. The interest arithmetic here applies equally.
Is this construction loan calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.