1
Mortgage & Loans
HELOC Calculator — Home Equity Line of Credit Limit & Payment
How much you can borrow against your home — and what the payment looks like in both the draw and repayment phases
A HELOC (home equity line of credit) is a revolving line of credit secured by your house — not a single lump sum, but a reusable credit limit you can borrow against, repay, and borrow against again, much like a credit card backed by your home equity but at a far lower rate. The whole reason to model it separately is its two distinct phases. First comes the draw period (usually 10 years), when the line is open: you pull cash as you need it, most lenders charge interest only on the outstanding balance, and the open credit replenishes as you pay it down. Then the line closes to new borrowing and flips into the repayment period (commonly 10–20 years), when whatever you still owe is amortized into full principal-and-interest payments. This calculator sizes the line and shows the payment in both phases.
That revolving, draw-then-repay structure is what sets a HELOC apart from its fixed sibling. A home equity loan hands you the full amount once and charges a fixed payment from day one — no draw period, no reusable limit, no variable rate; if you want that lump-sum-and-lock route instead, model it on the Home Equity Loan Calculator. The defining trait of a HELOC, by contrast, is that the rate is variable: it's almost always quoted as Prime plus a margin, so every Federal Reserve move ripples straight into your interest-only payment.
Sizing the line. Lenders cap how much credit they'll open using CLTV (combined loan-to-value) — every mortgage lien on the property added together and divided by the home's value, with a typical ceiling near 85% (sometimes 80%, occasionally 90%). To find your limit, multiply the home's value by that CLTV ceiling, then subtract everything you already owe on the property; what's left is the credit line you can open:
Available line = (home value × CLTV%) − balances already secured by the home.
Worked example. A $400,000 home with $250,000 still owed on the first mortgage and an 85% CLTV ceiling: the bank will allow total liens up to 400,000 × 0.85 = $340,000, and subtracting the existing $250,000 leaves a $90,000 line. Your raw equity is 400,000 − 250,000 = $150,000, but the credit limit is capped at $90,000 — and remember it's a limit, not a debt, so you owe interest only on what you actually draw.
The payment, phase by phase. Draw $80,000 at 7.5% during the draw period and the interest-only cost is just the balance times the monthly rate: 80,000 × (0.075 ÷ 12) = $500/month, a figure that floats up or down as you borrow more, pay down, or as Prime shifts. When repayment begins, that same $80,000 amortizes; over a 20-year repayment at 7.5% the payment jumps to roughly $644/month. Budgeting off the cheap interest-only number is the classic trap — it retires zero principal, so the eventual payment can leap 30–60% the moment the draw period ends, and a rate hike on the variable line only sharpens the jolt.
This tool provides informational estimates only, not a loan offer or financial advice; your actual CLTV limit, rate, draw terms, and payment are set by your lender.
📖 See also: What Is a HELOC and How Does It Work?
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Current equity = home value − mortgage balance • Max HELOC line = (home value × CLTV ÷ 100) − mortgage balance • Monthly rate r = APR ÷ 12 ÷ 100 • Interest-only payment (draw period) = amount drawn × r • Repayment P&I = D × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1), where D = drawn, n = repayment months
📰 Formula
• Current equity = home value − mortgage balance • Max HELOC line = (home value × CLTV ÷ 100) − mortgage balance • Monthly rate r = APR ÷ 12 ÷ 100 • Interest-only payment (draw period) = amount drawn × r • Repayment P&I = D × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1), where D = drawn, n = repayment months
🧪 Worked examples
2
Example 2
3
Example 3
4
Example 4
⚠️ Common mistakes
- Budgeting off the cheap interest-only draw payment and ignoring the bigger P&I repayment payment.
- Confusing your total home equity with the amount a lender will actually let you borrow (CLTV caps it).
- Forgetting the first mortgage balance counts toward CLTV, not just the new HELOC.
- Treating the variable HELOC rate as fixed — the payment moves when Prime moves.
💡 Tips
- Plan around the repayment-phase P&I payment, not the interest-only draw payment, so the shift doesn't blow your budget.
- Lower your draw amount if the line pushes your combined LTV near the lender's cap — you keep more borrowing room and a cushion.
- Because the rate is variable, leave headroom for Prime rate increases that raise your payment mid-draw.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/heloc-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How is the maximum HELOC amount calculated?
Max line = (home value × CLTV ÷ 100) − current mortgage balance. On a $400,000 home with $250,000 owed and an 85% CLTV limit, that's 400,000 × 0.85 − 250,000 = $90,000.
What is CLTV and why does it cap my line?
CLTV is combined loan-to-value — all mortgage debt on the home (first mortgage plus the new HELOC) divided by the home's value. Lenders typically allow up to 80–85%, so your existing balance eats into how much new credit you can open.
How much equity do I need for a HELOC?
Most lenders want you to keep at least 15–20% equity after the line is open, which is the flip side of an 80–85% CLTV cap. If you owe more than that share of the home's value, there may be no room for a HELOC.
How does a HELOC differ from a home equity loan?
A HELOC is a revolving line: you draw, repay, and redraw against a credit limit during the draw period, usually at a variable interest-only rate. A home equity loan is the fixed-rate, lump-sum alternative — you take the whole amount once and pay fixed principal-and-interest from the start. Model that route on the Home Equity Loan Calculator; use this page for the revolving line.
Why is my HELOC payment so low at first?
During the draw period most HELOCs are interest-only, so you pay only the rate on the balance you've drawn — no principal. Because the line revolves, paying a chunk back frees that credit to borrow again, but the outstanding balance never shrinks on its own, which is why the payment jumps once repayment begins.
What happens when the draw period ends?
The line stops letting you borrow and enters the repayment period, where the balance amortizes into principal-and-interest payments over the remaining term (often 10–20 years). That P&I payment can be 30–60% higher than the interest-only one.
How is the interest-only payment figured?
Interest-only payment = amount drawn × (APR ÷ 12 ÷ 100). Draw $80,000 at 7.5% and the monthly payment is 80,000 × 0.00625 = $500. Pay down or draw more and it changes.
Is a HELOC rate fixed or variable?
Almost always variable. HELOC rates are usually Prime plus a margin, so when the Federal Reserve moves and Prime changes, your rate and payment move with it. Some lenders offer a fixed-rate lock on a portion of the balance.
Does a HELOC affect my first mortgage?
No — a HELOC is a separate second lien on the home. Your existing first mortgage payment and rate stay the same (check it on the Mortgage Payment Calculator); the HELOC adds its own payment on top, and both balances together count toward your CLTV. If your goal is rolling high-rate balances into the line, the Debt Consolidation Calculator shows whether the swap actually saves money.