Because HELOCs usually have variable interest rates that fluctuate with the Prime Rate, your monthly payment can change dramatically from month to month, even if you never draw another dollar.
Real Estate
How to Calculate HELOC Interest Monthly
During the draw period, your HELOC payments are purely interest-based. Here is the exact mathematical formula to anticipate your monthly bill.
Published: April 17, 2026
Understanding the HELOC Draw Period
A Home Equity Line of Credit (HELOC) works like a credit card tethered to your house. During the initial 10-year "draw period," you usually only have to pay interest on the money you borrow.
The Formula: How HELOC Interest is Calculated
Most banks calculate HELOC interest using a Daily Periodic Rate. The interest accrues every single day based on your average daily balance.
Step 1: Find the Daily Rate
Take your Annual Percentage Rate (APR) and divide it by 365. For example, if your APR is 7.5%, your daily rate is 0.075 / 365 = 0.000205 (or 0.0205%).
Step 2: Find the Daily Interest Charge
Multiply the Daily Rate by your outstanding balance. If you owe $30,000, your daily interest charge is $30,000 * 0.000205 = $6.15 per day.
Step 3: Calculate the Monthly Bill
Multiply the daily interest charge by the number of days in your billing cycle (usually 30 or 31). For a 30-day billing cycle, your payment is $6.15 * 30 = $184.50.
HELOC vs Home Equity Loan
If the math above stresses you out, you might be better suited for a Home Equity Loan. A Home Equity Loan gives you a lump sum upfront with a fixed interest rate and fixed monthly payments, much like a traditional mortgage.
In a rising interest rate environment, a fixed home equity loan protects you from ballooning monthly payments. However, a HELOC provides more flexibility, as you only pay for what you actually withdraw.
Frequently Asked Questions
It is typically calculated daily based on your average daily balance. The formula is (Annual Rate / 365) * Average Daily Balance * Days in the Billing Cycle.
No, you only pay interest on the amount of funds you have actually withdrawn (your outstanding balance), not your total credit limit.