If you own your home and you are weighing an accessory dwelling unit, you have probably already done some quiet math at the kitchen table. An ADU is a real construction project, and the question underneath it is usually the same: where does the money come from without wrecking the loan you already have? A cash-out refinance is one of the common answers, and it deserves a clear look before you commit.

This is not a pitch for the lowest number you can find. A cash-out refinance for an ADU works when the whole picture works: the equity, the new payment, the fees, the timeline, and how long you plan to stay. We will walk through each piece in plain English so you can decide whether this fits your situation.

What a cash-out refinance actually does

A cash-out refinance replaces your current mortgage with a new, larger one. You receive the difference between the new loan amount and what you still owe, paid to you in cash at closing. The Consumer Financial Protection Bureau describes it the same way: you take out a bigger mortgage and pocket the gap.

That cash can fund an ADU, which is where the value sits for many homeowners. You convert equity that has been sitting still into a second living space that can house a parent, an adult child, or a renter. The trade is straightforward. Your mortgage balance goes up, and so does your monthly payment, in exchange for money you can use now.

The reason a cash-out refinance gets compared to other options is that it touches your primary mortgage. You are not adding a second loan on top. You are resetting the first one. That can be the right move or the wrong one depending on the rate you already hold, which we will get to.

How much equity you can pull for an ADU

Lenders cap how much you can borrow against your home using loan-to-value, or LTV. It is the size of the loan divided by the appraised value of the property. The cap is what protects you from borrowing your home down to nothing.

On a conventional cash-out refinance, the common ceiling is 80 percent of your home's appraised value for a one-unit primary residence. So if your home appraises at $400,000, the new loan would typically max out near $320,000. Whatever you still owe comes out of that first, and the rest is what you could take as cash.

Veterans have more room. A VA-backed cash-out refinance can go up to 100 percent of the appraised value, according to the Department of Veterans Affairs. If you served and you have the entitlement, that is a benefit you earned, and it can change the math on an ADU considerably. It is worth checking before you assume the conventional 80 percent ceiling applies to you.

A quick example. Say your home appraises at $450,000 and you owe $200,000. On a conventional loan at 80 percent LTV, the new loan could reach $360,000, leaving roughly $160,000 in cash before fees. That is real ADU money. The appraisal sets the ceiling, so the number you have in your head may not be the number the loan supports until the appraisal comes back.

Using a cash-out refinance for property improvements

Building an ADU is a property improvement, and that matters for two reasons.

The first is appraisal. A well-built ADU can add value to your property, which can soften the long-term cost of borrowing against it. That outcome is not assured and it varies by market, but a permitted, legal unit is generally treated differently than an unpermitted addition. Permitting is local. Your city or county sets the rules on size, setbacks, parking, and whether a unit can be rented at all, so that homework happens before the loan, not after.

The second reason is taxes. The IRS allows you to deduct home mortgage interest only on debt used to buy, build, or substantially improve the home that secures the loan, under Publication 936. Building an ADU on the property generally fits the "substantially improve" test, while using the cash for something unrelated would not. There is also a cap: interest is deductible on up to $750,000 of qualifying home acquisition debt ($375,000 if married filing separately) for debt taken on after December 15, 2017. This is not tax advice, and your situation is your own, so confirm the details with a tax professional. The point is that what you do with the cash affects how the loan is treated.

The CFPB's guide to using home equity is a neutral, plain read on the trade-offs, and it is worth ten minutes before any decision.

The part most people skip: your existing rate

Here is where the lowest advertised number becomes the trap rather than the prize.

A cash-out refinance replaces your whole mortgage. If you are holding a rate that is lower than what you would get today, refinancing the entire balance to fund an ADU can cost you far more over time than the cash is worth, even if the new payment looks manageable. The headline rate on the new loan tells you almost nothing on its own. What matters is the blended cost across your full balance and the years you will carry it.

So the honest question is not "what rate can I get." It is "what does this cost me in total, given the rate I already have, the fees, and how long I plan to stay." Sometimes the answer is that a cash-out refinance is clearly the right tool. Sometimes the answer is that touching your first mortgage would be expensive, and a different path protects the rate you are sitting on. A good loan officer will run both and show you the difference instead of steering you toward the bigger loan.

We say no to plenty of these for exactly this reason. If the refinance costs you more than it gives you, that is worth knowing before you sign, not after.

Running your own break-even math

You can do a useful version of this yourself with numbers you already have. You do not need a market rate to do it.

Start with the fees. A refinance carries closing costs, often a few percent of the loan amount, covering the appraisal, title, and lender charges. Add them up. Then look at how your monthly payment changes. If the new payment is higher, multiply the monthly increase by the number of months you expect to stay in the home. Add that to the fees. That total is roughly what the ADU money is costing you through the loan.

Now weigh it against what the ADU gives you: rental income, housing for family you would otherwise pay for elsewhere, or added property value. If the value clearly clears the cost, the refinance earns its place. If it is close, slow down. The math should be boring and it should be yours, built on your own payment and your own timeline, not a forecast about where rates are headed.

VA cash-out refinance for an ADU

If you are a veteran, the VA cash-out program deserves its own look. It can reach up to 100 percent of your home's appraised value, which is more equity access than a conventional loan typically allows. The home must be one you occupy as your primary residence, and you will need a Certificate of Eligibility to confirm your entitlement to the lender. You can request a COE through a lender, online, or by mail, and the VA's eligibility page lays out the service requirements.

This is a benefit tied to your service, and it is owed to you, not a favor. If an ADU is the goal and you have VA entitlement, the higher LTV ceiling can mean the difference between a project that pencils out and one that does not. It is the first thing to check, not the last.

A small, safe first step

You do not have to decide anything today. The smallest useful step is to pull two numbers: your current mortgage balance and a realistic estimate of your home's value. With those, a loan officer can sketch a rough LTV and tell you whether there is enough room for the ADU you have in mind, and whether a cash-out refinance is even the right tool given the rate you hold.

If you want a second set of eyes on the math, you can talk it through with a GoodLoan loan officer. We are licensed under our NMLS ID, we are VA-approved, and we would rather tell you the refinance does not make sense than sell you one that does not. There is no commitment in a conversation, and you will leave it knowing more than you did.

Frequently asked questions

Can I use a cash-out refinance to build an ADU?

Yes. The cash from the refinance is yours to use, and funding an ADU is a common reason homeowners choose this route. Because building an ADU is a property improvement, the interest may also be deductible under IRS Publication 936, though you should confirm your own situation with a tax professional.

How much equity do I need for a cash-out refinance?

On a conventional cash-out refinance, lenders generally let you borrow up to 80 percent of your home's appraised value, so you need enough equity to cover what you still owe plus the cash you want, within that ceiling. A VA-backed cash-out refinance can reach up to 100 percent of the appraised value for eligible veterans, per the Department of Veterans Affairs.

Will a cash-out refinance change my interest rate?

It can. A cash-out refinance replaces your existing mortgage entirely, so the new loan carries its own rate and terms. If your current rate is lower than today's, refinancing the full balance can raise your long-term cost even when the cash is useful, which is why the total cost matters more than the headline number.

Is the interest on a cash-out refinance tax deductible?

Interest is generally deductible only on debt used to buy, build, or substantially improve the home that secures the loan, up to a $750,000 cap for debt taken on after December 15, 2017, according to IRS Publication 936. Building an ADU on the property usually fits that test, but a tax professional should confirm the details for your return.

What does a VA cash-out refinance require?

You will need to meet the VA's service and occupancy requirements and provide a Certificate of Eligibility. The home must be your primary residence. You can request a COE and review the rules on the VA eligibility page before you apply.

How do I know if a cash-out refinance is worth it for me?

Add up the closing costs and any increase in your monthly payment over the years you plan to stay, then weigh that total against what the ADU gives you in rental income, family housing, or added value. If the value clearly clears the cost, it earns its place. A GoodLoan loan officer can run that math with your own numbers.