Will a hard plastic iPhone 5 case fit an iPhone 5S?

I've ordered an iPhone 5s, and I want to buy a case for it, but the one I want is sold as for the iPhone 5, will it work or will I be wasting my money?

If it fits on iphone 5.it will fit on 5s too.

Yes it will.

By the way check this review I've found it pretty much answers all of your questions about the new Iphone.
http://watchtvonl.blogspot.co.il/2013/09/apple-iphone-5s-at-review.html

Yes it would fit but do make note of the different LED flash modules. The 5 has 1 & the 5s has 2 top & bottom.

The exact precise dimensions of both phones are 123.8 x 58.6 x 7.6 mm, so yes itll definitely fit.