Why does the UK tax year start on 6 April each year?

It All Started with a Calendar Change

To understand the origin, we need to go back to 1582, when Pope Gregory XIII introduced a shift from the Julian Calendar (named after Julius Caesar) to the Gregorian Calendar (named after… well, you get it).

The Julian Calendar had served well for over 1600 years. It used 11 months of 30 or 31 days and one shorter February. But it ran 11½ minutes behind the solar calendar each year, and by the late 1500s it had fallen 10 days behind.

So, Europe switched to the Gregorian Calendar, which corrected this by occasionally skipping leap years (unless the century is divisible by 400). But the UK, having recently fallen out with the Catholic Church, refused to adopt the Pope’s reform.

Britain Falls Behind Europe — Literally

For the next 170 years, the UK and other holdouts like Russia stuck with the Julian Calendar. Over time, this created an 11-day gap between British and European calendars. By 1752, something had to change.

Meanwhile, in England and Ireland, major Christian holidays (like Christmas) served as “quarter days” for settling rents and debts. The first quarter day, “Lady Day” on 25 March (commemorating the angel Gabriel’s announcement to Mary), also marked New Year’s Day — and the start of the tax year.

1752: Britain Finally Makes the Switch

In 1752, Britain finally conformed to the Gregorian Calendar, officially moving New Year’s Day to 1 January and removing 11 days from the year. That September, 2 September was immediately followed by 14 September.

People were furious. They’d lost 11 days of their lives, yet were still expected to pay a full year’s worth of taxes. Crowds protested in the streets.

The Treasury’s Response: No Tax Left Behind

The Treasury, never one to lose revenue, kept the tax year at 365 days. So, the start of the next tax year was shifted from 25 March to 5 April.

Then in 1800, which would’ve been a leap year under the old Julian system but wasn’t under the Gregorian one, the Treasury made another adjustment: the tax year start moved again—this time to 6 April.

Why It Stuck

This odd practice ended in 1900, and since then, the UK has been stuck with 6 April as the official start of the tax year.

If the Treasury had continued adjusting for Julian leap years, we’d eventually align with the rest of the world… on 1 January 37901!

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