On a twin in the UK, you usually pay 10+5 mins flying time for taxying. 10 minutes worked back from takeoff time and a further 5 minutes from the landing time.
If your taxi time is more or less than 15 mins, it makes no difference therefore to the charge.
So per session, you have to add one quarter of one hour to your fees.
IIRC I went about £1200-1500 over on the ME CPL due to extra revision and a retest. Plus for the IR, waiting for slots meant some revision flights, a silly mess up at Yeovil (evil field!) meant a retest plus ferry flights for both attempts meant I was over the £10500 by (just a guess) about £2000-2500?
So about 20% contingency would be correct in *my* case. You will save a lot of cash for a first-time pass, but those people statistically are not in the majority.
Don't forget to budget the usual living costs stuff as well.
The best by far bit was the MCC with no cost overrun, masses of the instructor's time and loads of hours in the sim. Very good value
