Using own car for business (vat on private and business element)

Hi all
what method do you all use to calculate the vat on private fuel? (client of mine uses his car for business and his private use. when we calculate vat on these both what method do you adopt)
Thanks in advance
what method do you all use to calculate the vat on private fuel? (client of mine uses his car for business and his private use. when we calculate vat on these both what method do you adopt)
Thanks in advance
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