What your HELOC result shows
The first two figures answer what you can borrow. Lenders work to a combined loan-to-value limit across your existing mortgage and the new line, so your available credit is that percentage of the home’s value minus what you already owe — not your equity, which is a larger and more flattering number.
Then the two payments, and the number between them. During the draw period most lines require interest only, which is why a HELOC feels inexpensive: none of that money reduces the balance. When repayment begins the same debt has to be amortised over the remaining years, so the payment steps up — by a little if the repayment term is long, by a lot if it is short. That multiple is the figure to check before signing, because the decision people regret is not the borrowing; it is arriving at the repayment phase without having planned for it.
The stress test exists because a HELOC rate floats. Repayment may begin ten years from now at a rate nobody can forecast, so the honest presentation is a scenario at a higher rate rather than a single confident number.
How to use this HELOC calculator
- Home value and mortgage balance. Be conservative on the value — the lender’s appraisal governs, not an online estimate.
- The lender’s maximum combined loan-to-value. 80–85% is typical; anything higher usually comes with a worse rate and thinner protection if values fall.
- How much you actually intend to draw, not the full line. A line is approved capacity, and the cost only starts when you use it.
- Rate, draw period and repayment period from the offer. Ten years drawing and twenty repaying is the common shape.
- The stress test. Two points is a reasonable starting scenario; the point is to see whether the repayment payment is survivable at a rate you did not choose.
The two phases, and why the second one bites
A HELOC has a draw period, typically ten years, during which you can borrow, repay and borrow again up to your limit — like a credit card secured on your house. Minimum payments during this phase are usually interest only.
Then the line closes to new borrowing and the repayment period begins. Whatever is outstanding must now be repaid with principal, over a fixed number of years. Nothing about the debt has changed; only the obligation has. How big that step is depends almost entirely on the repayment term: spread over twenty years the increase is modest, while a ten-year repayment period can push the payment to roughly double. The calculator shows the actual multiple on your own figures rather than assuming it is alarming — and the figure is worth checking precisely because it is sometimes smaller than the warnings suggest and sometimes much larger.
Two protections are worth arranging in advance. Paying principal voluntarily during the draw period removes the cliff entirely, and the result above prices that — it is cheaper in total and it converts an unknown future payment into a known present one. Alternatively, some lenders allow you to fix a portion of the balance into a fixed-rate instalment loan during the draw period, which caps the rate risk on that slice.
HELOC or home equity loan?
A home equity loan is a lump sum at a fixed rate, repaid on a schedule from the first month — a second mortgage in the ordinary sense. A HELOC is a revolving line at a variable rate with the two-phase structure above.
The line wins when the need is uncertain or staged: a renovation running over months, a business with lumpy cash flow, a reserve you may never use. You pay for what you draw, and undrawn capacity costs little or nothing beyond any annual fee.
The fixed loan wins when the amount is known and the certainty is worth something — consolidating a specific balance, paying for a specific project. You know the payment and the end date on day one, which the line cannot give you. Compare the fixed option against the loan calculator, and remember that both are secured on your home.
What you are actually risking
Home equity borrowing is cheap because it is secured, and secured means the house. That is a genuine difference in kind from a card or a personal loan, not a technicality: default on unsecured debt damages your credit, while default on this can cost you the property.
Three consequences follow. Using a HELOC to consolidate credit card debt lowers the rate but converts unsecured debt into secured debt — a real saving, and a real transfer of risk, and worth doing only alongside whatever change stopped the balances rebuilding. Using one for a depreciating purchase means the debt outlives the thing it bought. And a lender can reduce or freeze an undrawn line if values fall or your circumstances change, which is precisely when you were counting on it.
Interest may be deductible when the money is used to buy, build or substantially improve the home securing the loan, and generally is not for other uses — the rules changed and are narrower than most people assume, so it is worth confirming for your own return rather than assuming.
None of that makes home equity borrowing a bad instrument. It is the cheapest credit most households can access, and for a project that genuinely adds value to the property it is often the right one. The point is that the pricing reflects the security rather than your creditworthiness, and the security is the thing you live in — so the test to apply is not whether you can afford the interest-only payment, which is easy, but whether you could afford the repayment payment above at the stressed rate, which is the obligation you are actually signing up for.
What this calculator assumes
- The full draw taken at the start and left outstanding. A real line is drawn and repaid unevenly, which changes the interest but not the structure.
- A constant rate in the main figures, with the stress test as the alternative. Real HELOC rates move with the prime rate throughout.
- Interest only during the draw period, which is the common minimum but not the only structure — some lines require a small principal component.
- No fees. Annual fees, appraisal costs and early-closure charges vary by lender and are not included.
- No change to the credit limit. Lenders can reduce or freeze a line, most often when values fall.
- Values held flat — no appreciation, so available credit here comes only from repaying the first mortgage.
These are planning estimates. The lender’s disclosure is the authority on the rate, the margin, the caps and the fees.
Home equity questions people ask
How much can I borrow against my home?
Most lenders lend up to 80–85% of the home’s value across all mortgages combined, so your available line is that percentage of the value minus what you already owe. Credit score, income and the property type all affect where within that range you land.
What happens at the end of the draw period?
The line closes to new borrowing and repayment begins, with principal and interest both due over a fixed term. If you have been paying interest only, the payment can multiply several times over — the figure above shows by how much on your numbers.
Are HELOC rates fixed?
Almost never. They are typically the prime rate plus a margin, so they move whenever prime does, including during the repayment period. Some lenders let you convert part of the balance to a fixed rate, which is worth asking about if the line will be outstanding for years.
Is HELOC interest tax deductible?
Only when the borrowing is used to buy, build or substantially improve the home that secures it, and subject to overall limits. Interest on money used for other purposes is generally not deductible. The rules are narrower than they once were, so confirm it for your own situation.
Can the lender cancel my line of credit?
A lender can reduce or freeze an undrawn line, most commonly if the property value falls or your financial position changes materially. That is worth remembering if the line is your emergency plan — an unused line is a promise rather than cash in an account.