How can I calculate a HELOC payment?

I am having a hard time understanding how to calculate a HELOC online.
Here is the situation. 205K HELOC line of credit with 150K just used. I am trying to figure out the payment. Lets say it is 10years at 5 %. What will the monthly payment be to have it paid off in 10years. You can assume that no additional money will be used on the line. What is the monthly payment and how do you come to this calculation? Thank You for your help
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A $150,000 laon at 5% interst for 10 years requires a payment of $1590.98 per month. You don't say if there is a base charge for maintaining the line of credit, so I can't speak to that.

Here is the calculation:

Determine your periodic rate, Pr. For a monthly payment, that simply means dividing the annual interest rate (as a decimal) by 12. For instance, the monthly periodic rate for a loan with an interest rate of 5% is: Pr = .05 / 12 = .00416666

Add 1 to that number, or Pr + 1. In this case 1.00416666

Raise that number to the power of the total number of months. DON'T GET SCARED; it's not that bad. Your scientific calculator should have a y^x button. eHow doesn't allow font formatting, but that would be a y with a small x on the upper right hand side of it.

So, if it was a 10 year mortgage, the number of payments would be 120. You would enter 1.00416666, hit the y^x button, then enter 120. The answer should be 1.647009

You can either write that number down, or store it in memory #1, if your calculator supports that.

You next want to subtract 1 from that number, so that would be:
1.647009 - 1 = 0.647009

Divide the smaller number into the larger number:

1.647009/0.647009 = 2.54557221

Multiply this 2.54557221 times the amount you want to borrow. If it's $150,000, it would equal $381,835.8315

Multiply $381,835.8315 times the periodic rate Pr:

$381,835.8315 * .0041666 = $1,590.98

This would be your monthly mortgage payment for a $100,000 loan for 30 years at 6% annual interest.
Step9In equation for, it looks like this:

Payment = (Pr+1)^#pmts. /((Pr+1)^#pmts.)-1) * Pr * Amount borrowed.