The calculation is gas production rate times gas price times production days per month times unit factor times your interest times times your royalty. I will assume that you own 40 acres because you don't say how many acres you own. I will also assume 3/16 royalty, $2.00 per mcf and 30.4 days per month (yearly average used in the oil business). Production taxes tend to be 1 or 2% for new gas wells in Oklahoma. I ignored the tax. Some leases include deductions for post production processing, etc, and I have ignored those. These costs tend to become significant when production declines or is small to begin with.
Here is the calculation: (500 mfc per day) times ($2.00 per mcf) times (30.4 days per month) times (2/3 unit factor or 66.7% unit factor) times (40 acres net / 640 acres gross) times (3/16 royalty) equals (your royalty payment per month).
500x2.00x30.4= $30,400 per month in gas revenue for the well
500x2.00x30.4x2/3=$20,266.67 per month for your tract
500x2.00x30.4x2/3x40/640= $1,266.67 per month for your acres (whole interest)
500x2.00x30.4x2/3x40/640x3/16= $237.50 per month for your royalty interest