I looked up a few papers and tables and found different perspectives. Generally, citalopram is allowed in the range of 20-40 mg, and zoloft 50-200. In one table, it was stated that the starting dose of citalopram is 20 and zoloft is 50, which is quite logical. From that, I can infer that 100 zoloft is 20+20 = 40 mg of citalopram, but it looks quite doubtful because 40 is the max dosage.
Furthermore, I found one study in which citalopram and zoloft were compared in the ranges of 20-40 and 50-100 respectively. In another study, they were 20-40 and 50-150. I’m still a bit confused. I took 40 mg for a couple of days and it didn’t strike me with a surge of apathy, but I felt it definitely more potent than just 100 mg of zoloft.
I’m not aware that you can even do that kind of comparison. Those are two different active ingredients, there is a very good chance they’ll do very different things in your brain.