How much can I borrow with a HELOC, and what is CLTV?

Lenders limit your combined loan-to-value (CLTV), the total of all mortgages on the home divided by its value, usually to 80 to 90 percent. Your available credit is the home value times that CLTV cap, minus the balance on your first mortgage. For example, a $400,000 home at an 85 percent CLTV supports $340,000 of total debt; if you still owe $250,000 on your first mortgage, about $90,000 is available to draw.

What happens if my draw is larger than my available credit?

The calculator does not cap or change the amount you enter. It still shows the draw and repayment payments for the amount you typed, and it flags that the draw exceeds your available credit so you can see it. In practice a lender would not approve a draw above your available credit, so treat the flag as a sign to lower the draw or increase your equity.

What is HELOC payment shock?

It is the jump in your monthly payment when the draw period ends. During the draw period you typically pay interest only, which is small. When repayment begins, that same balance must be paid off in full over the repayment term, so the payment can rise sharply overnight. This calculator shows both payments and the increase between them.

Why does the payment go up so much after the draw period?

During the draw period an interest-only payment never touches the principal, so when repayment starts you still owe the entire balance and now have to amortize it over a fixed number of years. Paying off, say, a $50,000 balance over 20 years is a far larger payment than just covering its monthly interest.

Does this calculator account for a variable rate?

No. It models a single constant rate so the two-phase structure is clear. Real HELOCs are variable and the rate usually rises after any introductory period, which means your actual repayment payment and payment shock could be larger than the estimate here. Treat this as a best case on rate.

HELOC Calculator

See how much you can borrow against your home equity at your lender's CLTV cap, plus a home equity line's interest-only draw payment, its much larger repayment payment, and the payment shock between the two phases.

Home value

Current market value of your home. Drives your equity and how much you can borrow.

First mortgage balance

What you still owe on your existing first mortgage. Leave at 0 if the home is paid off.

Max CLTV

Combined loan-to-value cap the lender allows across all mortgages. Often 80 to 90 percent.

Amount drawn

The balance you owe on the line. Payments are based on this, not your full credit limit.

Interest rate

Annual rate. Modeled as constant, though real HELOCs are variable and usually rise after an intro period.

Draw period

years

Years you can borrow and pay interest only. The balance can stay flat the whole time.

Repayment period

years

Years to fully pay off the balance after the draw period ends.

Extra principal during draw

Optional principal paid each month during the draw period. Leave at 0 for interest-only.

X f in

Available credit

$90,000.00

Home value times max CLTV, minus your first mortgage balance. The most you could draw.

Max total debt at CLTV: $340,000.00
Current home equity: $150,000.00
Current LTV: 62.50%
Draw vs available credit: Within available credit
Payment shock: $84.89
Draw-period payment: $333.33
Repayment-period payment: $418.22
Payment increase: 25.47%
Balance entering repayment: $50,000.00
Total interest over the life: $90,372.57

Monthly payment by phase

Assumptions

Available credit is your home value times the max CLTV, minus your first mortgage balance, floored at 0. CLTV (combined loan-to-value) is the cap a lender allows across all mortgages on the home, commonly 80 to 90 percent. The calculator also shows the max total debt the cap allows (home value times CLTV), your current equity (home value minus the first mortgage), and your current LTV (the first mortgage as a percent of home value, before the HELOC). If you enter a home value of 0, current LTV is shown as 0 rather than dividing by zero.
The amount drawn is used exactly as entered; it is never capped. If it is larger than your available credit, the calculator flags that but still shows the payments for the amount you entered, since a real lender would not approve more than the available credit.
The rate is modeled as constant for the whole term. Real HELOCs are variable: the rate floats with an index, and after any low intro period it usually rises, so a real borrower's payment shock is often larger than shown here.
During the draw period you pay interest only on the outstanding balance, plus any optional principal you choose to add. Any extra principal reduces the balance that enters repayment; with interest only and no extra principal, the balance stays flat and the full drawn amount carries into repayment. The balance entering repayment is always between 0 and the amount you drew.
When the draw period ends, the remaining balance fully amortizes over the repayment term as a fixed-payment loan, using the same amortization engine as the mortgage calculator.
Payment shock is the repayment-period payment minus the draw-period payment, the central risk this calculator exists to show. It can be negative if you paid down enough principal during the draw that the repayment payment ends up smaller than your draw-period payment. A negative payment shock therefore means your monthly payment falls when repayment begins rather than jumping.
Total interest over the life is the interest accrued during the draw period plus the interest on the repayment-phase amortization. Interest is computed monthly on the outstanding balance and rounded to the nearest cent.
All figures are in nominal dollars and are not adjusted for inflation, and the draw and repayment periods are treated as whole years.
Not modeled: a variable or adjustable rate that changes over time, closing costs, annual or inactivity fees, the tax deductibility of HELOC interest, lender-required minimum draws, and the timing of when within the draw period you borrow.
This is an estimate for educational purposes only, not financial, legal, or tax advice. Your lender's terms, rate changes, and fees will differ. Consult a qualified professional and your lender for numbers specific to your situation.

How it works

A home equity line of credit (HELOC) is really two loans wearing one name, and the gap between them is the thing worth understanding before you sign. It runs in two phases.

Draw period (often 10 years). You can borrow against the line up to your limit, and the required payment is typically interest only on whatever balance is outstanding:

draw payment = outstanding balance × (annual rate ÷ 12)

Because an interest-only payment never touches the principal, the balance can sit flat for the entire draw period. You can choose to pay extra principal, and this calculator lets you, but the minimum is interest only.

Repayment period (often 20 years). Borrowing stops, and the balance you are left with must be fully paid off over the repayment term. That is a standard amortizing loan, the same math as a mortgage:

repayment payment = balance × r(1 + r)^n / ((1 + r)^n − 1)

with r the monthly rate and n the repayment months. This calculator computes it with the same amortization engine the mortgage and refinance calculators use, so the payment and the payoff are exact and the formula is never duplicated.

Payment shock is the whole point:

payment shock = repayment payment − draw payment

For an interest-only draw, you enter repayment still owing the entire balance, so the jump is large. Paying extra principal during the draw shrinks the balance that carries over, which shrinks (or even eliminates) the shock.

Worked example

On a $400,000 home with $250,000 still owed, an 85% CLTV cap supports $340,000 of total debt, so about $90,000 is available to draw. This example draws $50,000 at a constant 8%, with a 10-year interest-only draw and a 20-year repayment:

Draw payment = $50,000 × (8% ÷ 12) = $50,000 × 0.00666667 = $333.33/month, interest only.
Nothing is paid down, so the balance entering repayment is the full $50,000.
Repayment payment = the amortizing payment on $50,000 at 8% over 20 years = $418.22/month.
Payment shock = $418.22 − $333.33 = $84.89/month, a 25.47% jump the month repayment begins.
Total interest across both phases is about $90,372.57: roughly $40,000 of interest-only payments over the 10-year draw, plus about $50,373 amortizing the balance over the next 20 years. You borrow $50,000 and pay back far more, because the draw period is ten years of pure interest before a single dollar of principal comes off.

Now pay an extra $300/month of principal during the draw instead. The balance entering repayment falls to $14,000, the repayment payment drops to $117.10, and the “shock” actually goes negative: your draw payment of $633.33 was already higher than the repayment payment. Principal paid early is what defuses the shock.

The rate is the catch

This model uses a single constant rate so the two-phase structure is clear. Real HELOCs are variable. The rate is tied to an index (commonly the prime rate) plus a margin, it can reset monthly, and after any low introductory rate it usually moves up. That matters for the direction of the risk: a real borrower’s repayment payment, and the shock, are frequently larger than this calculator shows, not smaller. Treat the constant-rate result as a best case on rate, and stress-test a higher rate before relying on the line.

Edge cases and what is not modeled

At a 0% rate the draw payment is zero and the repayment is straight-line (balance ÷ repayment months). Closing costs, annual fees, and any lender-required minimum draw are not modeled. Interest is computed monthly on the outstanding balance and rounded to cents, so totals match a real monthly statement rather than a continuous approximation.

The equity layer reports your available credit (home value × CLTV − first mortgage balance, floored at 0), your current equity, and your current LTV alongside the payments. The amount you draw is never capped: if it is larger than your available credit, the calculator still computes the payments on the amount you entered and simply flags that it exceeds what a real lender would approve, so the numbers always reflect your input rather than a silently reduced figure.

Sources

Consumer Financial Protection Bureau, credit reports and scores
Federal Reserve, What you should know about home equity lines of credit
Standard fixed-rate amortization for the repayment phase; interest-only accrual for the draw phase.

Frequently asked questions

How much can I borrow with a HELOC, and what is CLTV?: Lenders limit your combined loan-to-value (CLTV), the total of all mortgages on the home divided by its value, usually to 80 to 90 percent. Your available credit is the home value times that CLTV cap, minus the balance on your first mortgage. For example, a $400,000 home at an 85 percent CLTV supports $340,000 of total debt; if you still owe $250,000 on your first mortgage, about $90,000 is available to draw.
What happens if my draw is larger than my available credit?: The calculator does not cap or change the amount you enter. It still shows the draw and repayment payments for the amount you typed, and it flags that the draw exceeds your available credit so you can see it. In practice a lender would not approve a draw above your available credit, so treat the flag as a sign to lower the draw or increase your equity.
What is HELOC payment shock?: It is the jump in your monthly payment when the draw period ends. During the draw period you typically pay interest only, which is small. When repayment begins, that same balance must be paid off in full over the repayment term, so the payment can rise sharply overnight. This calculator shows both payments and the increase between them.
Why does the payment go up so much after the draw period?: During the draw period an interest-only payment never touches the principal, so when repayment starts you still owe the entire balance and now have to amortize it over a fixed number of years. Paying off, say, a $50,000 balance over 20 years is a far larger payment than just covering its monthly interest.
Does this calculator account for a variable rate?: No. It models a single constant rate so the two-phase structure is clear. Real HELOCs are variable and the rate usually rises after any introductory period, which means your actual repayment payment and payment shock could be larger than the estimate here. Treat this as a best case on rate.

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Last reviewed June 2026. For education, not financial advice.