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.

Hi! First off, I am not a medical doctor nor am I a licensed psychiatrist, so please supercede any of my information with what your personal doctor/care team says.

Second, when considering the therapeutic range of medication you cannot just look at increasing the mgs. The way you've calculated these trial dosages are following a raw formula (base starting dose multiplied by some number) and that isn't taking in account the efficacy curve. That's a really wordy way to put it, sorry. Consider that 100mg is around a 33% increase from the 50-200 range. You'd be looking for a similar 33% increase in the 20-40 range (27ish mg).

Basically, just because 100mg Zoloft was your starting dosage, you'd more realistically be looking at a dosage of 25-35mg Citalopram.

And depending on what the medication you're looking at is made of, dosages can get wild and may not compare using the efficacy curve or my i-just-woke-up math. If you're already looking at papers to determine personal dosages, try following along with the lowest dosage, see if it has effect, then take the next dosage up. Starting right at the 40mg may be too intense for your system overall, and could make your body intolerant of Citalopram if you go too hard. It's much, much better to start lower than you think you need and work up. Best of luck!

Source: I have experience in drug research and development. Pictured below is my scratch math. +50 for each 33% increase on Zoloft, +7ish for each 33% increase on Citalopram. If anyone catches a mathematical error please lmk! :)