The 45p Rule: Why "Guesstimating" Mileage is Costing You a Fortune

It is Sunday night. You have had a long week. You want to watch the football, spend time with the family, or just have a beer.

Instead, you are sitting at the kitchen table with a pile of Screwfix receipts and a crumpled logbook, trying to remember where you drove last Tuesday.

“I went to that boiler job in Croydon… that’s about, what? 20 miles round trip?”

You scribble “20 miles” in the book. You move on.

You just lost money.

The HMRC Maths (The 45p Rule)

As of right now, HMRC allows you to claim tax relief of 45p per mile for the first 10,000 miles of business travel in personal vehicles (or for reimbursements).

That sounds like small change. It isn’t.

Let’s look at the “Croydon Job” again.

You guessed 20 miles. But if you actually checked Google Maps, or the odometer, maybe the route you actually took (avoiding the roadworks on the High Street) was 24 miles.

• You claimed: 20 miles x 45p = £9.00
• Actual driving: 24 miles x 45p = £10.80

You lost £1.80 on one trip.

Now multiply that by 5 days a week. That’s £9 a week. Multiply that by 48 working weeks.

That is £432 a year, per van, that you effectively threw in the bin.

And that is just from under-guessing by 4 miles a day.

The “Shoebox” Problem

1. You forget trips: The quick run to the wholesalers to get a part you forgot? You probably didn’t write that down. That was 6 miles (£2.70) gone.
2. You guess distances: We like round numbers. We write “10 miles,” not “11.4 miles.” Those decimals add up.
3. HMRC is watching: If you get audited, and your logbook just lists “10 miles, 10 miles, 20 miles,” it looks suspicious. HMRC likes exact figures.

The problem isn’t that you are bad at maths. The problem is that manually logging miles makes it impossible to be accurate, unless you’re a robot.

The “Set and Forget” Fix

This is exactly why we designed Tiny Telematics to plug into the OBD-II port.

The OBD-II port is the computer brain of your vehicle. It doesn’t “guess” how far the wheels turned. It knows.

When you plug a Tiny tracker in, the Sunday Night ritual changes:

1. You open the app.
2. You click “Export Mileage Report.”
3. You send it to your accountant.

The report doesn’t say “About 20 miles.” It says: Start: 08:00 AM (Postcode A) -> End: 08:45 AM (Postcode B). Distance: 24.3 miles.

It Pays for Itself

We aren’t promising to make you a millionaire. We are trying to stop you from leaving free money on the table.

If our tracker catches just 10 miles a week that you would have otherwise forgotten or under-claimed, that is £4.50 back in your pocket.

Over a month, that covers the cost of the subscription.

Stop guessing. Stop writing in logbooks on Sunday nights. Let the van do the maths for you.