Yes there is a clue.
To-hit-chance in percentage is shown when targetting, up to 95% (higher is impossible). This means there's a 5% chance you'll miss and a certain chance you'll fumble (depending on Luck).
To hit chance (for ranged) works roughly like this...
Your skill (in percentage) - 30 = base to hit. Add 8% for every point of perception. Subtract 4% for every hex distance. Subtract 1% for every Armor Class point of the opponent. Change for modifiers (skills, darkness, sniper scope), but that's the basic computation.