Somewhere in the middle of a construction draw schedule sits a line item most sponsors barely glance at during underwriting: the interest reserve. It rarely gets debated the way hard costs or contingency do. Then, twelve months into a build, it becomes the reason your equity partner gets a call they were not expecting.
An undersized construction loan interest reserve does not fail quietly. It fails at the worst possible moment, when the project is mid-build, the lender is unwilling to increase the facility, and the only source of additional capital is the equity that already thought its job was done.
The Line Item That Triggers a Capital Call
The interest reserve exists to cover the carrying cost of the construction loan during the period before the hotel opens and starts generating revenue. It is capitalized into the loan itself, drawn down month by month as interest accrues on the outstanding balance. On paper, it is a formality. In practice, it is one of the few line items in the capital stack with almost zero tolerance for schedule slippage.
When the reserve runs dry before the certificate of occupancy is in hand, the borrower is contractually obligated to keep making interest payments. That obligation does not pause for punch list items or a slow FF&E install. Someone has to write that check, and it is rarely the lender.
How Reserves Are Sized
Most interest reserves are sized off three inputs: the projected loan balance over time, the interest rate, and the construction timeline. Multiply the average outstanding balance by the rate, apply it across the projected number of months to substantial completion, and add a modest cushion. That is the math most pro formas run.
The problem is not the math. The problem is the assumption sitting underneath it: that the timeline used to size the reserve is the timeline the project will actually follow. Reserves sized to an optimistic schedule are reserves sized to fail. If the underwriting timeline assumes fourteen months and the reserve is calculated accordingly, there is no room for the project to run sixteen or eighteen. Lenders are not in the business of padding reserves against risks the sponsor has not flagged, which means the burden of realism falls on the development team building the pro forma in the first place.
What Delays Do to It
Delays do not erode the interest reserve in a straight line. They compound it. Every additional month of construction adds another month of accruing interest at the same time it pushes back the date the hotel starts generating the revenue that was supposed to replace debt service. Schedule drift and interest reserve depletion move together, and the relationship gets worse the longer a project sits under construction, because the loan balance is typically largest in the later months when most of the capital has been drawn.
A 90-day delay is not an abstraction on a Gantt chart. It has a direct, calculable effect on carrying costs, and by extension on projected IRR. The same forces that create schedule drift, whether it is a permitting delay, a redesign triggered by a value engineering pass gone wrong, or a subcontractor default, are the forces that quietly consume a reserve that was never built with slippage in mind. For a closer look at how these delays cascade through a project timeline, see how schedule drift affects IRR across the life of a build.
Protecting the Reserve
Protecting the interest reserve starts well before the loan closes. It starts with a construction schedule that reflects how the project will actually be built, not how it looks in a lender presentation. That means realistic float, honest assumptions about permitting timelines in the specific jurisdiction, and a GC who is willing to say a date is aggressive before the loan is sized around it.
Early GC involvement protects the capital stack precisely because it forces this conversation to happen at underwriting instead of month nine of construction. A contractor brought in after the loan closes has no incentive, and often no ability, to challenge the assumptions baked into the reserve calculation. One brought in during design and financing can flag schedule risk before it becomes a capital call. This is part of why early GC involvement matters as much to the finance team as it does to the field team.
It is also worth remembering that the cheapest bid is often the most expensive schedule. A GC who wins on price by underestimating scope or overpromising on duration is setting the stage for the exact delays that consume an interest reserve. The hidden costs behind the lowest bid tend to show up as schedule overruns long before they show up as change orders.
Getting the Reserve Right Before It Matters
An interest reserve sized to an unrealistic schedule is not a reserve. It is a deferred equity call with a delayed timestamp. The fix is not a bigger contingency line buried in the pro forma. It is a schedule and cost basis built on realistic assumptions, reviewed before the capital stack is finalized. A disciplined pro forma and feasibility review is where that discipline starts, well before the first draw request ever reaches the lender.