How often can I use fuel additives on my car?

Why would you use an additive ? Today's gas has everything your car needs already in it .Dont waste your money on additives . If it makes you feel better once a year put a bottle of fuel system cleaner in to help clean out any accumulated junk in injectors and lines . All of the fuel system cleaners are the same so no product recommendations just get a name brand.

It's more important to keep the detritus swilling up the bottom of your tank from getting sucked up. So NEVER drive a dinosaur below 1/4 tank!

What do you use? Some are safe and some are junk or worse. An occasional dose of Techron is all I would use.

I commonly used STP branded (as it is sold at Kwik Trip's here) and I last used the fuel injector & carburetor cleaner, about 6k miles ago (car is at 205k now). I'll for sure use Techron in small doses.

Use Techron at the recommended dose if you want it to work. You could use it once or twice a year depending on how much you drive.

Techron is indeed more effective as it's concentrated solvents instead of cheap filler. That's why STP et al decided to offer higher concentrations at double the price years ago. Fuels have detergents in them now so I very rarely chase an issue requiring an additive. I really think keeping fuel level above 1/4 tank is the most important precaution with older vehicles.