chattychat, sorry but me thinks you are wrong. i have not yet had to do a calc and i have not read up on it in detail, but my understanding is that : quakedog, i assume that your taxation works normally, ie you are being taxed on 80% of : 3.5 % (3.25% if approved maintenace plan) on the full value of the vehicle INCL vat. check with your HR dept. some people do not bother with a logbook as they know their private mileage is significant. they either consent to a voluntary over deduction of tax to 100% of above in order to avoid having to pay in tax on the 20% on assessment. (or they just pay on assessment) under certain conditions, the 80% inclusion rate can be reduced in order to alleviate the monthly tax burden, but only where business travel is significant. for you, it would make sense to claim, considering your mileage split. it works really simple as far as i know, no tables of fixed and variable costs etc (this is where chattychat went wrong, these only apply to CAR ALLOWNACES where no actual record of expenditure was kept) your TOTAL mileage is 23100. your business mileage is 15600. therefore your business component is 15600/23100 = 67.53% . IF you have paid taxes as i assumed above at 80%, then you will be able to claim back 12.47% (80 minus 67.53%). i will actually read up on it now, you have sparked my interest....