How long should one wait to have another botox after having a botox and filler treatment?

I have been injecting Botox for over twenty-two years and fillers of all kinds for more than thirty years. My personal experience echoes what has been reported in the medical literature that combining the use of a neuromodulator, such as Botox, with a filler for areas such as the scowl lines, worry lines and crow's feet, may lead to prolonged benefits. Botox typically lasts between four to six months, with luck up to seven months, when used alone. Fillers, such as Juvederm or Restylane, may yield results that last on average about eight months. However, when both Botox (or the other neuromodulators) and fillers are used to treat the dynamic and static components, respectively, of these regions, results tend to last longer--approximately a year. Accordingly, I personally prefer to treat these areas with both. Both injections can be done done in one session--my preference--or separated by about two weeks. 

Botox typically last 3-4 months and fillers can last 8-12 months, though some patients do metabolize it quicker, its best to consult with your physician to determine your aesthetic desires

Most patients have Botox every 4 months. However, different patients metabolize Botox at different rates, so you will have to see what is right for you. However, 4 months is a good estimate. For fillers, 8 months to a year is a good estimates. However, so newer fillers such as Juvederm Volume have been shown to last up to 2 years or more, so it really depends on which filler you are having and which areas you are having injected.Good Luck.