In Chrono Trigger, characters who use techs - single, double, and triple - are meant to incur a percentage-based penalty to their speed on their next turn, causing their ATB bar to fill more slowly. However, due to a programming error, the first character listed in the game's script for that tech will not be penalized. Thus, single techs carry no ATB penalty.

You can view all of the intended penalties on this spreadsheet (courtesy of Pseudoarc).

This also means that in the case of a double tech, only one character will incur the penalty; two characters in the case of a triple tech. The penalties for each character are hard-coded, so you cannot make a different character take a penalty based on whose menu it is executed from, for example.

The below tables illustrate which characters suffer penalties from which techs, and how much.