Normally it would be -525 for the left eye and -450 for the left.

Normally it's "one notch less for contacts" at those powers, so the right
eye -4.75 becomes -4.50.

In the left eye, -050 astigmatism is approximated by half, to -025 sphere.

-5.25 -0.25 = -5.50 ("spherical equivalent")

"One notch less" than -5.50 is -5.25.

You might prefer -450 in both eyes if you're over 40.

Individuals vary, so we put contacts on and then measure for glasses. The
"overrefraction" should be zero ("plano").

-MT, OD

An eyecare professional can advise you better in a face to face situation
than any of us can do in this newsgroup.

This said, here is some information which can be useful when visiting such a
professional.

For the right eye your specialist probably takes a S-4.50 and for the left a
S-5.00
The -0.50 astigmatism should NOT be compensated by adding half off its power
to the spherical power of the contactlens, it simply is of no use for your
visual acuity.
However your specialist could consider a toric softlens for the left eye.

To all eyecare professionals in this newsgroup I want to inform you of the
possibilities for patients/customers living outside the US to buy VERY
easily contactlenses WITHOUT any eye examination.
Over here for instance, drugstores are selling softcontactlenses (one size
fits all) without any problem again WITHOUT any prescription such as needed
in your (US) country.
Softcontactlenses from several brands (BL,CooperVision,CIBA etc..) are also
sold on internet, again WITHOUT the need of a prescription or a consultation
of an eyecare professional.

So, questions like the above most of the time sounds to me like they are
posted by '' do it yourself fitters''
Please keep in mind this is an international newsgroup.