Hi, having just nicely got back from a P&O cruise. The way it worked is as follows; the on board credit is credited to your account from the first day, after this point all purchases are debited to your account until the final night, the resulting balance then has the Portunus Club discount subtracted to give the final account figure.
So essentially, you can look at it this way Total Spend minus OBC minus Portunus Club percentage discount.
I hope this adequately explains it. .....Bob.
Take note of one thing about on board credit. If this is £100 per cabin it means £50 each, so make sure that each of you use your cruise card for purchases. If you only use one card you will only get £50 of you final bill and not £100.
I have not found this to be the case if you have linked accounts -i.e both paid on the same credit card. The balance is simply transferred to whoever is paying, even if it is a credit. If you pay independently then then you could be correct.