@ranaanuj052
The flat rate mentioned in the link that you have posted is for Northern Residents Deductions
Or the other flat rate charges mentioned by CRA are for deductions by the employer and paid tax-free to employees or officers as reimbursement for motor vehicle expenses incurred while travelling for business purposes, using their personal vehicle.
Self Employed individuals must keep all their receipts. They can use the detailed log book or the simplified log book but not flat rate.
