Numbers don't add up. Is GA worthless?

I've had this issue/problem ever since I started Google Analytics. Now, I'm not a smart man, but shouldn't my 7-day active users be around 112k instead of 100k? (16,000 x 7 = 112,000).

And shouldn't my 30-day active users be around 480,000k? (16,000 x 30 = 480,000). Are all analytic platforms this imprecise? Am I missing something? I'm also seeing this inaccuracy with my Android and web property too. Thanks