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Why does the tax year start in April ?

We talk about tax year end and 'ISA Season' a lot at Wealthify, but we've never really thought about why we start the tax year on the 6th April. So we did a little digging.
Illustration of hand holding magnifying glass looking at a calculator and a piece of paper.  Why does the tax year start in April?
Reading time: 2 mins

For complete transparency – back in the 1500’s the tax year started on 25th March. We couldn’t pin-point exactly why, but it ranges from religious, to agricultural reasons. So, on that note, let’s begin!


It all started back in medieval times when people wanted to make sure they didn’t lose out on tax revenue. (Tax revenue was a thing back then too!)  

In 1582, Pope Gregory XIII, ordered that the Julian calendar, which was created by Julius Caesar, be replaced with his preferred Gregorian calendar, named after…well, himself.

Pope Gregory XIII and Julius Caesar

The Julian calendar had worked perfectly well for the previous 1,600 years or so and had consisted of 11 months of 30 or 31 days with a 28 (or 29) day February. However, changing this started a knock-on effect – which meant by 1752, we’d lost 11 days.  

To ensure the 11 days didn’t affect their tax-revenue, it was decided to add it to the end of that tax year. So, in 1753, the tax year ended on 4th April.

If you’re still with us…

Moving forward to 1800, this would have been a leap year under the old Julian calendar, but it wasn’t in the Gregorian one. So, they extended the tax year again, meaning in 1800, the tax year ended on the 5th April - and it has started on the 6th April ever since!   

More transparency: This information was produced using our research of tax year end.  If anyone who was around in 1582 has a different view, we’d be happy to hear it.  

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