How long does Botox in the chin last?

Like many other areas of the face that are treated with Botox, results last about 3-4 months for the chin, or possibly a little longer. The number of units needed to address your concern would be determined by your medical injector during your consultation, although since you are a "first timer", it may be on the lower end so that your reaction to treatment can be gauged first. 

Botox generally lasts 3-4 in the chin.  Everyone one is different, results can possibly last up to 6 months. Best of luck.