Partial Month Calculations

I would like to hear from people who have experience in developing
software for payroll:

If a person works from 01/01/09 to 23/05/09 and his/her wages are
$48000 per annum.

Would his/her earnings be:

(A)
$4000*4+23/31*$4000=$12000+$2967.74

or

(B)
$4000*4+23/365*$48000=$12000+$3024.65 (Non Leap Year)

$4000*4+23/366*$48000=$12000+$3016.40 (Leap Year)

Is there a general consensus/ common practice on this?
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