Tripcatcher uses whole miles when calculating mileage expenses, hence tripcatcher restricts data entry to whole miles. One of the reasons Tripcatcher uses whole numbers is so the mileage can be submitted to Xero or Receipt Bank using their respective Expense APIs. By passing a whole number as the quantity of the mileage and the mileage rate (e.g. 45) as the unit price, then the Expense API can handle the mileage claim as an expense.
The verbal advice we’ve had from HMRC is that mileage can be entered to a decimal point or rounded to the nearest whole number. HMRC also said the treatment should be consistent and in the client’s favour. We’ve written to HMRC asking for the advice to be confirmed in writing, or that HMRC add the information to the HMRC website. (They’ve acknowledged that guidance on rounding trip distances is not on the HMRC website). We are still awaiting the reply.
The Tripcatcher distance calculator (where you enter the to and from locations) rounds to the nearest integer, 1.9 is rounded to 2 and 1.4 is rounded to 1.