The Haynesville Shale is one of the largest unconventional gas plays in the US. It is also one of the deepest, with wells reaching more than 10,000 ft below ground. This uncommon depth and overpressure lead to initial gas pressures of up to 12,000 psi. The reservoir temperature is also high, up to 300 °F. These pressures are uniquely high among shale gas reservoirs, and require special attention when modeling. We show that the method developed by Patzek et al. (2013) scales cumulative gas production histories of individual wells such that they all collapse onto one universal curve. Haynesville wells can take months or years for flowing tubing pressure to stabilize, so we modified the universal curve to take this delay into account. We have written a custom Pressure–Volume–Temperature (PVT) solver to calculate gas properties at the high reservoir pressure and temperature. When we apply the Patzek et al. scaling theory to 2199 individual wells in the Haynesville, we find 1546 wells have entered exponential decline due to pressure interference. We use a simple physical model to determine the time to interference, for wells with geologic parameters typical of the Haynesville, and use this time to interference to determine a field-wide stimulated permeability. Using this permeability, we arrive at an estimate of the times to interference for the remainder of Haynesville wells, and obtain production forecasts for all individual wells.