Compute HELOC payments through both the interest-only draw period and the full principal + interest repayment period, plus your maximum credit line.
Max credit line available
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Draw-period payment (interest only)
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Repayment payment (P + I)
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Total interest (life of loan)
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Total paid
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The two phases that catch borrowers off guard
A home equity line of credit does not behave like a normal loan, and that surprises people. For the first stretch, usually ten years, you are in the draw period. You can pull money out up to your limit, and the lender typically bills you interest only on what you have borrowed. The payment feels small. Then the repayment period begins, the line closes to new draws, and you start paying down principal and interest together over the remaining years. That second payment can be noticeably higher, and a borrower who budgeted around the draw-period number gets a jolt. This tool models both numbers so you see the jump before you sign, not after.
The other thing worth understanding is that a HELOC almost always carries a variable rate, quoted as the Wall Street Journal Prime Rate plus a margin set by the lender. When the Federal Reserve moves, your payment moves. The 8.5% in the default example is a reasonable mid-cycle figure, but run it again a point or two higher to stress test yourself. A rate you can afford today is not guaranteed for the full thirty years.
What your home equity actually unlocks
Lenders cap your total borrowing against the home using a combined loan-to-value ratio, or CLTV. Most allow somewhere between 80% and 85%. The math is simple: take the appraised value, multiply by the CLTV cap, then subtract whatever you still owe on the first mortgage. On a $500,000 home at 85% CLTV with a $300,000 mortgage, the ceiling is $425,000 minus $300,000, which leaves $125,000 of available credit. You do not have to draw all of it, and a smart borrower rarely does. The line is there; the obligation only starts when you tap it.
A $80,000 draw at 8.5%, phase by phase
Say you draw $80,000 against that $125,000 line at an 8.5% rate, with a ten-year draw period and a twenty-year repayment period. During the draw years, interest only, your monthly payment is the balance times the monthly rate: $80,000 times 0.085 divided by 12, which works out to about $567. That is all you owe each month, though paying interest only means the $80,000 principal is still sitting there untouched when the draw period ends.
| Step | Figure |
|---|---|
| Amount drawn | $80,000 |
| Draw-period payment (interest only) | $567 per month |
| Interest paid across 10 draw years | $68,000 |
| Repayment payment (principal and interest, 20 years) | $694 per month |
| Interest paid across 20 repayment years | $86,622 |
| Total interest over the life of the line | $154,622 |
| Total paid (principal plus interest) | $234,622 |
The headline buried in that table is the total interest of roughly $155,000 on an $80,000 draw. Interest-only payments feel cheap, but stretching them across a full decade means you never reduce the balance, so repayment starts at the same $80,000 you began with. Pay a little principal during the draw years and you shrink both the later payment and the lifetime interest considerably.
When the interest is deductible
Since the 2017 Tax Cuts and Jobs Act, HELOC interest is deductible only when the borrowed money is used to buy, build, or substantially improve the home that secures the line, and only if you itemize on Schedule A. Pull $80,000 to renovate a kitchen or add a room and the interest generally qualifies, subject to the overall mortgage-interest cap. Use the same $80,000 to consolidate credit cards or fund a vacation and the interest is not deductible at all, even though the loan is secured by your house. The IRS spells this out in Publication 936. Keep records that tie the draw to the improvement; the deduction follows how the money was spent, not how the loan was titled.
Who should use a HELOC instead of a cash-out refinance?
A HELOC fits when you want flexible access to equity over time, for instance a multi-stage remodel where you draw as bills arrive and pay interest only on what you have used. A cash-out refinance fits when you need a single lump sum and want to lock a fixed rate. If your existing first mortgage already carries a low fixed rate, a HELOC lets you tap equity without disturbing it, which can be the deciding factor when current refinance rates are higher than the rate you already hold.
What happens to my payment when the draw period ends?
It almost always rises, often sharply. During the draw period you may pay only interest, but once repayment begins you amortize the full outstanding balance over the remaining term. In the example above the payment moves from about $567 to about $694, and that is on a balance that never went down. Borrowers who paid only the minimum can face a much larger increase, sometimes called payment shock. The fix is to pay extra principal voluntarily during the draw years so the balance is smaller when amortization kicks in.
Can the lender freeze or cut my line?
Yes. Lenders can reduce or suspend a HELOC if your home value drops sharply or your credit deteriorates, and many did exactly that during the 2008 downturn. An open line is not the same as guaranteed cash. If you are relying on a HELOC as an emergency backstop, understand that the access can shrink precisely when you most want it, so do not treat undrawn credit as a substitute for an actual cash reserve.