Somewhere on your tax return there is a box for business mileage, and right now it is either empty or holding a guess. You did the driving. Client visits, site meetings, the trip to the supplier two counties over. You just never wrote any of it down, and the only record you have is a general sense of "quite a lot" and a door pocket full of car park receipts.
If you forgot to track your business mileage this year, you are in good company, and you are not out of options. The record you need is sitting in the one place you have been keeping up to date all along.
What the missing miles are worth
If you are self-employed, business miles come off your profits at HMRC's flat rate: 45p a mile for journeys up to 5 April 2026, and 55p a mile from 6 April 2026, on the first 10,000 miles in a tax year, then 25p a mile after that. Six thousand miles in the 2025/26 tax year is £2,700 you can set against your profits. The same six thousand miles since April is £3,300. Leave the box empty and that money stays with HMRC.
Guess, and you have a different problem. A round number with nothing behind it is the kind of figure an enquiry picks on. HMRC's own guidance for people whose records are missing is to do your best to provide figures and to tell HMRC that they are estimated. A better answer is to go and find the evidence.
Why a GPS app can't help you now
The usual advice is to download a mileage tracker. Fine for next year. Useless for this one, because a GPS tracker only knows about journeys made after you installed it. As far as it is concerned the past never happened, and no amount of swiping trips into "business" will bring it back.
Your calendar was in the car with you
Every client visit you made was a meeting first. It sat in your Google or Outlook calendar with a date, a time and an address, put there before you left the house. That is a record made at the time, by you, for a reason that had nothing to do with tax, which is about as good as evidence gets.
TravelSync reads that calendar and turns it back into journeys. When you connect it, it goes through the last two years of your diary, works out the real road distance for every meeting with a physical address, and builds the log you never kept. Home to the client, client to the next client, the last one back home. The current tax year and the whole of the one before it, on the day you sign up.
What to do if you forgot to track your business mileage
Connect your calendar, tell it where home and the office are, and let it run. Setup takes about five minutes. What comes out the other end:
- Every journey dated, with where it started, where it ended, and the distance by road rather than as the crow flies.
- The right HMRC rate on each journey for the date it happened: 45p before 6 April 2026, 55p after, with the 10,000-mile threshold tracked across the year.
- Duplicates collapsed, so a meeting that sits on two calendars is counted once.
- A CSV you can hand to your accountant or work straight into the return. Filter it by calendar if the school run lives in the same diary as your clients.
No GPS, no app running on your phone, and nothing new to remember from here on, because it keeps logging from the meetings you were going to book anyway.
Jamie, who built TravelSync, ran it on his own diary for two years before it was a product. "What used to be a dreaded afternoon of receipts, route-guessing and suspiciously round numbers is now a download button, with every business mile already logged and the right HMRC rate applied to each journey."
What the rebuild can't do
It rebuilds what your calendar shows. A trip you made on the spur of the moment and never booked won't appear, and neither will a meeting you deleted afterwards. Video calls are ignored, which is the point, but a site visit you booked as "chat with Dave" with no address will be skipped along with them. It routes from the home and office addresses you give it today, so if you moved during the two years, check the earlier months against the old address.
The export is a practical record for you and your accountant, built from evidence you already had. It is not a certified tax document. It is still your return, and if you have an accountant, they should see the figures before HMRC does.
Is it too late to claim for last year?
Usually not. The online 2025/26 return is not due until 31 January 2027, and the rebuild covers every month of it. If you have already filed a return without your mileage, you can amend it for up to 12 months after its filing deadline, so a 2024/25 return can still be corrected until 31 January 2027, and the rebuild reaches back into that year too. Beyond the 12 months, you can write to HMRC and claim overpayment relief for up to four years after the end of the tax year concerned.
The miles happened. The calendar kept the receipts. All that was missing was something to add them up.
Start a free 14-day trial, connect your Google or Microsoft calendar, and your last two years of journeys are rebuilt while you make a cup of tea. No card needed. Start your free trial.