Short version: an interest reserve is a pool of money, sometimes set aside by the lender and sometimes just budgeted by you, that covers your monthly interest payments during a fix and flip so you are not paying out of pocket every month while the house produces no income. It is not free money. It is your money, spent on carry, and knowing how it works keeps your cash flow honest. FMC Capital finances fix and flip loans for investors. Call 412-990-2941 or request a quote.
What an interest reserve actually is
A fix and flip loan is interest-only, and the property does not earn a dime while you are renovating it. That creates a simple cash flow problem: every month you owe an interest payment, but the house is not paying you back until you sell. An interest reserve is how that gap gets managed. In its most formal version, the lender holds back a set number of months of interest from the loan proceeds at closing and draws your monthly payment from that pool automatically, so you never write a check during the rehab. In its looser version, there is no formal holdback and the reserve is simply the cash you have set aside to make those payments yourself.
Either way, the concept is the same. You are pre-funding the carry so a slow month does not turn into a missed payment. It sits right alongside the other costs of borrowing, and it is worth reading how it fits into the total in our breakdown of fix and flip closing costs.
How a lender-held reserve is calculated
When a lender builds a formal interest reserve, the math is straightforward. They take your loan amount, apply the interest rate, and multiply by the number of months they want covered. Say your loan is 300,000 dollars at an interest rate of 10 percent. Monthly interest is the loan times the rate divided by twelve, which is 300,000 times 0.10 divided by 12, or 2,500 dollars a month. If the lender sets aside a six month reserve, that is 15,000 dollars carved out of your proceeds and held to cover payments one through six.
Two things follow from that. First, the reserve reduces the cash that actually reaches your project, because it is taken from the loan. Second, you are paying interest on the full loan including the reserved portion, so a reserve is a convenience, not a discount. It smooths your cash flow, it does not lower your cost.
The interaction most investors miss
Here is where it gets subtle. On many rehab loans your monthly interest is charged only on the funds that have actually been drawn, not on the full approved rehab budget sitting undrawn. When that is the case, your early payments are smaller because the rehab money has not all been released yet, and a six month reserve might actually stretch to cover seven or eight months of real payments. But some loans charge interest on the full balance from day one regardless of what you have drawn. That difference, sometimes called Dutch versus non-Dutch interest, changes how far your reserve goes and how much the loan really costs. It is important enough that we wrote a full explainer on Dutch versus non-Dutch interest and what you actually pay on undrawn rehab, and you should read it before you assume your reserve will last.
Interest reserve versus minimum interest
Do not confuse the interest reserve with the minimum interest guarantee, because they pull in opposite directions. The reserve is about having enough set aside if the project runs long. The minimum interest guarantee is about the lender collecting a floor of interest even if you pay off fast. If you flip in three months but the loan carries a six month minimum interest guarantee, you owe those extra months whether or not you used a reserve. One protects you against a slow project, the other protects the lender against a fast payoff. We break down that second one in our guide to minimum interest and interest guarantees, and together they define the real cost of your carry.
A full example from closing to sale
Put it together on a real deal. You buy a house for 200,000 dollars with a 60,000 dollar rehab, borrowing 240,000 dollars total across purchase and rehab draws. The lender sets a rate of 10 percent and builds a six month interest reserve. Full monthly interest at the top of the loan would be 240,000 times 0.10 divided by 12, or 2,000 dollars, so a six month reserve is about 12,000 dollars held from proceeds.
Because your rehab funds release in draws, your actual interest in months one and two might only be 1,400 dollars while the rehab is partly undrawn, climbing toward the full 2,000 dollars as the draws complete. So your 12,000 dollar reserve might comfortably cover the whole project even if it runs the full six months. If you finish and sell in month four, the unused reserve is simply not spent, though you should confirm whether any minimum interest applies. Either way, you never wrote a monthly check, and your cash stayed in your pocket for the next deal. Run your own carry against your timeline on the deal calculator so you know how many months of reserve you actually need.
Should you want a reserve on your deal?
- Yes, if your cash is tight. A reserve means a slow permit or a delayed draw never threatens a payment, which protects your credit and your relationship with the lender.
- Maybe not, if your cash is deep. Since you pay interest on the reserved amount anyway, an investor with plenty of liquidity may prefer to keep those proceeds working in the project and just pay the monthly interest directly.
- Always, size it to the term. Match the reserve to a realistic project length. A reserve that runs out in month five on a seven month gut just recreates the cash flow problem it was supposed to solve.
The size of the reserve also moves with your rate and points, so it is worth understanding what drives your rate and points in 2026 and how your term length choice changes how many months of carry you should pre-fund.
Frequently asked questions
What is an interest reserve on a fix and flip loan?
It is a pool of money that covers your monthly interest payments during the rehab so you do not pay out of pocket each month while the house produces no income. It can be formally held back by the lender from loan proceeds, or simply budgeted by the investor.
Does an interest reserve cost extra?
No, but it is not free either. The reserve is your own loan proceeds set aside for carry, and you pay interest on that reserved amount just like the rest of the loan. It smooths cash flow rather than lowering cost.
How many months of interest should I reserve?
Match it to a realistic project timeline with a cushion. A six month reserve is common, but a full gut that will run seven to nine months should reserve accordingly so payments never lapse before the sale.
Is an interest reserve the same as minimum interest?
No. A reserve protects you if the project runs long. A minimum interest guarantee protects the lender by collecting a floor of interest even if you pay off early. They are separate features that both affect your total carry.
Financing a flip in 2026? We will structure the interest reserve to match your real timeline so your cash flow stays clean. Call 412-990-2941 or request a quote. FMC Capital, NMLS #1840537. We are a Pittsburgh-based brokerage serving real estate investors across Pennsylvania and additional states.