HELOC and Home Equity Loan Rates Explained: Prime + Margin vs Fixed Rates

A HELOC and a home equity loan both let you borrow against the value of your home, but they are priced in completely different ways. A HELOC usually carries a variable rate built from the prime rate plus a margin, while a home equity loan usually carries a fixed rate agreed at signing. This guide explains how each rate works, what moves it, and how to compare offers without chasing a headline number.

How a HELOC rate is built: prime plus margin

A HELOC rate has two parts. The prime rate is a widely published benchmark rate that moves when overall interest rates move. The margin is the extra amount your lender adds, and it is fixed for your line when you sign. Your HELOC rate is simply the two added together:

HELOC rate = prime rate + margin. If the prime rate is 7.50% and your margin is 0.50%, your rate is 8.00%. If the prime rate later rises to 8.50%, your rate becomes 9.00% — the margin does not change, the benchmark does.

Because the prime rate can move any month, your HELOC payment can move too. On a $50,000 drawn balance, an 8.00% rate means an interest-only payment of $50,000 × 8.00% ÷ 12 = $333.33 a month. That payment is not fixed: it follows the balance you have drawn and the rate in force that month.

How a fixed home equity loan rate is set

A home equity loan is a lump sum, and its rate is normally fixed at signing: the rate you agree on day one is the rate for the whole term, and your monthly payment never changes because of rate moves. That certainty is the main reason people choose it over a line of credit.

The payment follows the standard amortization formula, where the monthly rate is the annual rate divided by 12 and the payment covers both interest and principal from the first month. The table below shows what that means for a $100,000 loan over 15 years at three example rates — again, illustrations, not current rates:

Illustrative rates only. A 1% difference on this loan changes the payment by about $55 a month and the total interest by about $10,000.

Two things stand out. First, the rate matters more than most borrowers expect: 2% of extra rate costs roughly $20,000 of extra interest on this example. Second, the fixed payment is set in stone — if market rates fall after you sign, your rate does not fall with them unless you refinance.

What moves each rate

HELOC rates move with prime. When the prime rate rises, every HELOC priced off it rises by the same amount, usually at the next billing cycle. When prime falls, HELOC rates fall too. Two guardrails soften the ride: a lifetime cap sets the highest rate your line can ever reach, and a floor sets the lowest. Ask for both numbers in writing — the cap is what protects you in a rising-rate world.

Fixed loan rates move only for new loans. Once your home equity loan is signed, market moves do not touch it. But the rate offered to new applicants changes constantly with bond markets, lender costs, and demand, which is why two neighbors who borrowed months apart can hold very different fixed rates on similar loans.

Your margin and your fixed rate both reflect risk. A lower loan-to-value ratio, a stronger credit history, and a smaller loan relative to the home’s value generally earn a lower margin on a HELOC and a lower fixed rate on a loan. The lender, the property type, and whether the home is your primary residence matter too.

HELOC rate vs fixed loan rate, side by side

Neither structure is always cheaper. The cheaper choice depends on how much you draw, for how long, and where rates go next.

How to compare rate offers honestly

Headline rates mislead. Compare offers on the full package:

• The margin, not just today’s rate. Two HELOCs can show the same rate today with different margins — when prime moves, the lower-margin line stays cheaper.
• The cap and the floor. A low starting rate with a high cap can cost more over time than a slightly higher rate with a tighter cap.
• Introductory rates. Some lines open with a discounted rate for a few months, then revert to prime plus margin. Compare the revert rate, not the teaser.
• Fees. Application, appraisal, origination, and annual fees change the true cost even when the rate looks identical. Ask for the full fee schedule.
• The draw and repayment terms. A longer draw period means more years of interest-only payments; a shorter repayment period means a bigger second payment. The rate is only one input — run the whole loan through a calculator before you sign.

For a HELOC, that means checking your margin, cap, and floor, and testing what your payment becomes if prime rises 1% or 2%. For a fixed loan, it means comparing the fixed rate and the total interest over your chosen term — 10, 15, 20, or 30 years — not just the monthly payment.

Worked example: what a rate rise does to a HELOC payment

Take a $50,000 drawn balance. At an example rate of 8.00%, the interest-only payment is $333.33 a month. If prime rises 1%, the rate becomes 9.00% and the payment becomes $375.00. If prime rises 2%, the rate becomes 10.00% and the payment becomes $416.67 — $83.34 more a month than where you started, with no extra borrowing at all. That is the variable-rate trade-off in one table:

Illustrative rates only. Your payment also changes whenever your drawn balance changes.

All rates in this article are hypothetical illustrations used to show the arithmetic; they are not current rates, not quotations, and not a prediction of any lender’s pricing. Check the current rate, margin, caps, floors, and fees with the lender. All payments recomputed from the standard interest-only and amortization formulas.