This varies by lender but the absolute max you can take out is the equity you have in your house. For example, if your house is worth $500,000 and your mortgage balance is $400,000 then the largest HELOC you can have is $100,000. However, most lenders will only give you a fraction of that based on combined loan-to-value (CLTV). If the max CLTV is 90% then using the example above you could have a HELOC of $50,000.