Some advanced calculators also show variation, though the 74HC14 oscillator typically stays close to 50% unless R1 ≠ R2 in a different topology.
7400 Series Guide: 74HC14/74LS14 (Hex Schmitt-trigger inverters) 74hc14 oscillator calculator full
You don’t always need a web tool. Here’s a quick formula for Excel or Google Sheets: Some advanced calculators also show variation, though the