It literally just means "consider you to be brutal". Maybe "you're brutal" or "that's brutal" fits better for English speakers.
Interestingly both characters 狠 and 很 share a common meaning that they both mean "brutal", or "cruel". However in some scenarios brutal/cruel might be too much, maybe you can seek some thesaurus from the tangent of "很", meaning "very" (adj), "too much".
It's more like expressing "you win", but with the emotion saying "you only win because you over-do it brutally". But when it is physical rather then mental, 狠 would mean "aggressively" or "violently".
However, it can be used as a admiration between friends expressing "you accomplish this job in a awesome way, although that feels a bit overkill. 算你狠" -- In this sense that'll be more like "you're the man" kind of expression.