Construction Draw Interest During Construction Calculator

Purpose and model boundary

This model builds an eight-period construction draw schedule. It combines hard, soft, and other cost; allocates base cost between debt and equity; calculates interest during construction (IDC) and undrawn commitment fees; routes those financing costs to debt or equity; and reports any completion funding gap.

It is a construction-finance planning model, not a draw certificate, facility agreement, lender approval, construction guarantee, audit, solvency opinion, or investment recommendation. Debt eligibility and commitments are user assumptions and do not establish availability or legal entitlement.

Inputs and units

All costs, commitments, draws, IDC, and fees use one user-consistent currency scale, shown as currency millions. The schedule has exactly eight rows. Each row contains a unique text label, hard cost, soft cost, other cost, a debt-eligible fraction, and integer days in the period.

The base-cost selector chooses pro rata debt and equity, equity first, or debt first. Debt share applies to the pro rata route. The IDC basis is beginning debt or beginning debt plus half the current base debt draw. IDC and fees are capitalized within facility headroom or funded from equity. Actual/365 and Actual/360 select the annual accrual denominator.

Governing relationships

For row t, base construction cost is:

Base cost_t = Hard cost_t + Soft cost_t + Other cost_t

The current debt draw cannot exceed remaining facility headroom or the row's debt-eligible amount. Under pro rata funding, the requested debt amount is Base cost_t × Debt share. Debt-first requests the eligible amount before equity. Equity-first uses available equity first and requests debt for the residual, still subject to eligibility and facility headroom. The equity base draw is the remaining base cost after debt, capped by the remaining equity commitment.

The interest balance is:

Interest basis_t = Beginning debt_t

or

Interest basis_t = Beginning debt_t + Base debt draw_t / 2

IDC and the commitment fee are:

IDC_t = Interest basis_t × Annual interest rate × Days_t / Day-count denominator

Commitment fee_t = max(0, Facility limit - Prior cumulative debt - Base debt draw_t) × Commitment fee rate × Days_t / Day-count denominator

The day-count denominator is 365 or 360 according to the selected convention. In capitalized mode, debt-funded IDC and fees are the lesser of their total and the facility headroom remaining after the base draw. In equity-funded mode, this debt amount is zero. Equity funds the remaining IDC and fee amount up to its remaining commitment.

The row funding gap is unfunded base cost plus unfunded IDC and fees. Ending debt equals beginning debt plus the base debt draw plus capitalized IDC and fees. Realized debt share is total debt draws divided by total debt plus equity draws, or zero when both are zero.

Calculation sequence

1. Validate funding, IDC, and day-count selectors; bounded rates and commitments; and all eight grid rows.
2. Sum each row's three construction-cost categories.
3. Apply debt eligibility, funding priority, facility headroom, and equity commitment to the base cost.
4. Calculate IDC from the selected noncircular balance basis and day-count convention.
5. Calculate the fee on undrawn facility after the base debt draw.
6. Capitalize IDC and fees or fund them from equity, then record any amount not funded.
7. Roll cumulative debt and equity forward, sum totals, populate the cumulative draw chart, apply the derived numeric gate, and evaluate status.

Outputs and interpretation

The flow stages report base construction cost; cumulative debt and equity draws with their realized debt share; IDC and commitment fees; peak debt, ending debt, and facility headroom; and the final completion funding gap. Total debt draws include capitalized IDC and fees. Total equity draws include equity-funded construction costs and financing costs.

The chart compares cumulative debt and equity draws through the eight periods. It shows the modeled funding path, not certified construction progress or remaining lender availability under a real agreement.

Validation and status logic

The workbook evaluates status in this order:

Input-domain failure has first precedence, followed by derived arithmetic failure, then the completion-gap warning.

Assumptions and limitations

• Interest is noncircular. The average-debt route includes half the current base debt draw and excludes current-period capitalized IDC.
• Commitment fees apply to facility headroom after the current base debt draw.
• Facility availability is measured against cumulative draws. Repayment and recommitment are outside this construction-only model.
• Debt eligibility is a row-level cap and does not establish lender approval or tax deductibility.
• Retainage, VAT, letters of credit, multiple facilities or currencies, floating-rate curves, hedging, contingency release, and monthly draw certification are excluded.
• The model reports a gap and does not create an automatic plug.
• All shipped costs, rates, commitments, and period rows are synthetic illustrations.

Restrictions and non-computing states

The grid must contain exactly eight complete rows. Labels must be text from 1 through 60 trimmed characters and unique without regard to case. Hard, soft, and other cost must be nonnegative. Debt eligibility is from 0 through 1. Days must be an integer from 0 through 366. The debt share, annual interest rate, and commitment fee rate are from 0 through 1; debt and equity commitments are nonnegative.

Zero-day rows and zero rates are valid and accrue no financing cost. Zero commitments are valid but ordinarily produce a CHECK funding gap when costs remain. A quoted numeric or numeric period label fails the workbook's relational/type guard even if the input rules allow the underlying cell value.

Errors and warnings

A rejected entry means an option, scalar, or fixed-grid entry failed the published input rules. Workbook NOT VALID identifies an invalid active domain or unsupported derived arithmetic. Workbook CHECK retains the draw schedule while exposing unfunded construction cost, IDC, or fees. A connection or calculation-service failure is not a funding result. OK confirms arithmetic closure within the modeled commitments only.

Construction lending and completion-risk context follows the OCC Comptroller's Handbook: Commercial Real Estate Lending. Public infrastructure-finance context follows the FHWA P3 Toolkit primers. No lender term, external benchmark, project schedule, table, or proprietary dataset is embedded.