It all depends
Last August, I wrote a blog post about what it takes to be a good editor. In that post, I confessed that I could never remember the difference between “dependent” and “dependant”.
It took me 10 months, but I’ve now managed to get my head around the distinction. In case you also struggle with it, here’s a quick rundown:
dependant (noun) A person who relies on another, especially a family member, for financial support.
It’s easier to save money when you have no dependants.
dependent (adjective) Contingent on or determined by, requiring someone or something for financial or other support, unable to do without.
He had become dependent on drugs.
My technique for remembering which is which is to picture a little pet ant who is my dependant, since the noun form has the word “ant” in it. (Hey, I didn’t say it was a good technique.)
By the way, if you’re American, you don’t need to worry about this – “dependent” is the correct spelling of both forms for you. British English is heading that way too, but at the moment it’s safest to differentiate, at least in formal writing.