The implementation of a dynamic frequency divider in a fully flexible amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) technology on a sub-15 \mu \text{m} polyimide substrate is presented. This frequency divider is regenerative and is also known as a Miller divider. In this letter, it is implemented using only a Gilbert cell with minimum-size LO transistors. Including the bias network, it has only eight transistors. Using a 6-V supply voltage, it operates up to 3.93 MHz, consumes 328 \mu \text{W} , and has a speed over power Figure-of-Merit (FOM) of 12.0 MHz/mW. To the best of our knowledge, this FOM is the highest reported for circuits in this class of flexible TFT technologies.