Based on Planar Microwave Engineering by T. H. Lee
Typical error <10%, if parameters within the conditions. Error is less for 25 ohm to 100 ohm Z0.
Conditions: W>H, T<H.
Examples...
H=92um, W=100um, T=45um, Er=4.4
This calculator: Z0=57.6Ω, ADS LineCalc: Z0=59.6Ω, HFSS: Z0=61.9Ω
H=58mil, W=126mil, T=1.4mil, Er=4.5
This calculator: Z0=44.5Ω, ADS LineCalc: Z0=47.7Ω @1GHz, 50.0Ω @10GHz, HFSS: Z0=50.2Ω @1GHz, 51.8Ω @10GHz