You have extra money each month and two loans against the same house. Here is the rule that actually holds up: pay off whichever loan charges the higher rate first, and for most homeowners with a home equity line of credit, that is the HELOC.
Key Takeaways
- Rate, not balance, decides the order. A $40,000 HELOC at 8.5% costs more per dollar than a $320,000 first mortgage at 6.5%, so the HELOC comes first.
- On a $320,000, 6.5% first mortgage, an extra $200 a month saves about $105,429 in interest and cuts the loan by roughly 6 years 7 months — but only once the HELOC is gone.
- HELOC rates are variable and reset with the prime rate, so the gap between the two loans can widen without you doing anything.
- A HELOC in its draw period usually only requires interest-only payments — paying only the minimum lets the balance sit at full cost indefinitely.
- The first mortgage wins the order only in narrow cases: a fixed-rate HELOC priced below your mortgage rate, or a mortgage rate high enough to flip the comparison.
- Once one loan is paid off, redirect that entire payment to the other — never let a freed-up payment quietly become spending money.
Which should you pay off first: your HELOC or your first mortgage?
In most households the answer is the HELOC. A home equity line of credit almost always carries a higher, variable interest rate than a fixed-rate first mortgage, and every extra dollar you send toward the higher-rate balance stops more interest from accruing than the same dollar sent to the lower-rate loan. The order is a math question before it is a psychology question — figure out which loan is more expensive per dollar owed, then attack that one.
The exception shows up when someone locked a fixed-rate HELOC or home equity loan years ago at a rate below their current first-mortgage rate. That homeowner should flip the order. Check both rate sheets before assuming the HELOC automatically loses.
Why does the interest rate decide the order?
Interest is charged on the outstanding balance of each loan independently. Paying down principal on the loan with the higher rate removes more future interest per dollar than paying down the loan with the lower rate, even if the lower-rate loan has a much bigger balance. This is the same logic behind the debt avalanche method, just applied to two loans secured by the same property instead of a stack of unsecured debts.
A HELOC's rate is usually tied to the prime rate plus a margin, so it moves when the Federal Reserve moves. A fixed 30-year first mortgage does not move at all. That combination — variable and typically higher, versus fixed and typically lower — is why the HELOC is the default target.
How is a HELOC structured differently from your first mortgage?
A first mortgage amortizes on a fixed schedule: same payment, same rate, principal and interest split predictably every month until payoff. A HELOC is a revolving line, structured in two phases:
- Draw period (commonly 10 years): you can borrow, repay, and re-borrow up to the credit limit. Many lenders only require an interest-only payment during this phase.
- Repayment period (commonly 10–20 years): the line closes to new draws and converts to a fully amortizing loan, often at a higher required payment.
Because the draw-period minimum can be interest-only, a HELOC is the one loan in your stack that will not shrink on its own if you pay only what's billed. Every dollar above the interest-only minimum goes straight to principal, which is exactly why it rewards extra payments disproportionately.
What does the math look like side by side?
Here is a representative comparison. Loan basis: a $320,000 first mortgage at a 6.5% fixed rate, paired with a $40,000 HELOC balance at an 8.5% variable rate — a realistic pairing for a homeowner who financed a renovation with home equity.
| Loan | Balance | Rate | Monthly interest cost (rate ÷ 12 × balance) |
|---|---|---|---|
| First mortgage | $320,000 | 6.5% fixed | ≈ $1,733 |
| HELOC | $40,000 | 8.5% variable | ≈ $283 |
The mortgage's total monthly interest is bigger only because the balance is bigger. Per dollar of principal, the HELOC is costing 2 percentage points more every year it sits unpaid. Directing $300 a month of extra cash at the $40,000 HELOC clears it in roughly 11 years faster than doing nothing extra, and every one of those months of avoided 8.5% interest is money the 6.5% mortgage would not have saved you at the same payment size. Once the HELOC hits zero, redirecting that same $300 (now freed from HELOC billing) plus the original extra amount to the first mortgage keeps the compounding advantage going: on the $320,000, 6.5% mortgage, an extra $200 a month saves about $105,429 in interest and cuts the term by about 6 years 7 months, per the site's amortization table.
When does paying off the first mortgage win instead?
Run the comparison before assuming. The first mortgage should get the extra dollars first when any of these is true:
- Your HELOC or home equity loan has a fixed rate lower than your first mortgage's rate — some lenders offer this on smaller lines.
- Your first mortgage is an older loan at a rate well above today's market (a legacy 7%+ fixed loan next to a promotional-rate HELOC).
- Your HELOC is close to its draw-period end and the repayment-period payment is already affordable without acceleration, while the first mortgage still has decades of interest ahead of it.
Outside those cases, the higher-rate loan wins the order, and for the large majority of HELOC holders that is the HELOC.
What risk does the HELOC's draw period add?
The interest-only minimum is a trap disguised as flexibility. A homeowner who pays only the interest-only minimum for the full draw period arrives at the repayment period with the original balance untouched, then faces a fully amortizing payment calculated to clear that same balance in the shorter remaining window — a payment that can jump by hundreds of dollars a month with no warning beyond the loan documents. Treating the HELOC as "the loan with a low minimum payment" instead of "the loan with the highest rate" is the single most common reason homeowners get the payoff order backwards.
There's a second risk specific to variable rates: if prime rises while you're mid-payoff, the gap between your HELOC rate and your fixed mortgage rate widens further, which only strengthens the case for paying the HELOC first — it does not weaken it.
How do you automate the order once you've decided?
Set the extra payment to route automatically so the decision doesn't have to be remade every month. Two ways to do it:
- Set up a recurring principal-only auto-draft on the HELOC for the extra amount, on top of the required interest-only payment, timed a few days after your paycheck lands.
- Once the HELOC hits zero, cancel that auto-draft and immediately start (or increase) a principal-only auto-draft on the first mortgage for the same amount — the extra-payment calculator shows exactly how much time and interest a given monthly amount removes from the mortgage from that point forward.
If you'd rather see the two loans modeled side by side before committing, our HELOC payoff strategy guide walks through drawing up a payoff order for your specific rates and balances, and the earlier piece on HELOC vs. cash-out refinance for early payoff covers what to do if the HELOC's rate has climbed high enough that refinancing it into the first mortgage is worth pricing out.
What if you're worried about losing liquidity?
The honest objection to paying down a HELOC aggressively is that you're giving up a flexible credit line in exchange for equity you can't spend without reapplying. That's a real cost, not an imagined one. The way around it: keep a fully funded emergency fund in cash before accelerating either loan, and if your HELOC allows it, leave the line open (even at a $0 balance) rather than closing it, so the flexibility stays available if you need it later without a new application. Paying down the balance and closing the access are two different decisions — you only need to do the first one.
Frequently Asked Questions
Should I pay off my HELOC before my first mortgage?
Usually yes, because HELOC rates are typically variable and higher than a fixed first-mortgage rate. Compare your actual rate sheets first: if your HELOC's rate is lower than your mortgage's, pay the mortgage first instead. The higher-rate loan should always get the extra dollars.
Does paying off a HELOC first actually save more money than paying the first mortgage?
Yes, when the HELOC's rate is higher, because interest accrues per dollar of balance at that loan's own rate. A smaller balance at a higher rate can cost more per month, per dollar, than a larger balance at a lower rate — extra payments should target the rate, not the size of the loan.
What happens if I only make the interest-only minimum payment on my HELOC?
The principal balance never decreases. When the draw period ends, the loan converts to a fully amortizing payment sized to clear the untouched balance in the shorter repayment window, often producing a payment increase of several hundred dollars a month with little advance warning.
Can I send extra principal to both loans at the same time?
You can, but it's mathematically inferior to concentrating every extra dollar on the higher-rate loan first, then moving the full amount to the second loan once the first is paid off. Splitting extra payments feels balanced but leaves the more expensive debt outstanding longer than necessary.
Does the payoff order change if my HELOC has a fixed-rate option?
Yes. Some lenders let you lock a portion of a HELOC balance at a fixed rate. If that locked rate is lower than your first mortgage's rate, the mortgage should get the extra payments instead — always compare the actual rates, not the loan type, to set the order.
Where does a HELOC fit if I'm also paying off other debt, like a car loan or credit cards?
Line every debt up by interest rate, HELOC included, and pay the highest-rate balance first regardless of whether it's secured by the house or not. Credit cards and most personal loans typically carry higher rates than even an 8–9% HELOC, so they usually come before it in the order, not after.
Your next step
Pull your actual HELOC statement and your mortgage statement side by side and compare the two rates — that single comparison tells you the order. Then run the amortization calculator against each loan at your real balance and rate to see exactly how many months an extra $100, $200, or $300 removes, so you're automating a number you've verified instead of a guess.