Every year, as the UK approaches early April, conversations turn to tax returns, allowances and year-end planning. But have you ever stopped to wonder why the UK tax year runs from 6 April to 5 April, rather than lining up neatly with the calendar year?
The answer lies in a fascinating mix of history, astronomy and government pragmatism.
Back in the 18th century, Britain was operating under the Julian calendar, introduced by Julius Caesar in 45 BC. Much of Europe, however, had already transitioned to the Gregorian calendar, introduced by Pope Gregory XIII in 1582 to correct inaccuracies in the length of the year. Over time, the Julian calendar had drifted out of alignment with the solar year, creating a growing discrepancy between dates observed in Britain and those on the continent.
By 1752, the difference between the two calendars had reached 11 days. To bring Britain into line with Europe, the Calendar (New Style) Act was passed. In September of that year, 11 days were effectively skipped — 2 September was followed by 14 September — to correct the misalignment.
At that time, the legal New Year in Britain began on 25 March, known as Lady Day. This date was also significant for financial and administrative purposes, including taxation. So when the calendar shifted forward by 11 days, the government faced a practical problem: how to ensure a full year’s worth of tax revenue was still collected.
Rather than shortening the tax year and losing those 11 days of income, the Treasury adjusted the start of the financial year forward by the same 11 days. That moved the beginning of the tax year from 25 March to 5 April. Later, in 1800, a further adjustment was required because 1800 was not treated as a leap year under the Gregorian calendar (though it would have been under the Julian system). This created an additional one-day shift, pushing the start of the tax year to 6 April — where it remains today.
While it may seem quirky, this long-standing tradition has endured for more than two centuries. It’s a reminder that modern financial systems are often shaped by historical decisions made for practical reasons at the time.
Beyond the trivia value, the approach of the 5 April year-end is an important financial milestone. It marks the deadline for making use of annual allowances such as ISAs, pension contributions, capital gains exemptions and certain tax relief opportunities. Once the tax year closes, unused allowances are often lost and cannot be carried forward (with limited exceptions).
That’s why this period is more than just an interesting historical footnote — it’s a strategic opportunity.
The weeks leading up to the end of the tax year are an ideal time to review your broader financial position. Are your pension contributions aligned with your long-term retirement goals? Have you used your ISA allowance effectively? Is your investment strategy still appropriate given market conditions and personal circumstances? Are there opportunities to manage capital gains or income tax exposure more efficiently?
These are complex considerations that often benefit from professional insight. Tax rules change, thresholds move, and personal circumstances evolve. A coordinated conversation between you, your financial adviser and your accountant can ensure that your strategy is aligned, compliant and optimised for the year ahead.
So yes, the 6 April start date may make for a great trivia answer at your next dinner party. But more importantly, it serves as a timely reminder: the end of the UK tax year is one of the most valuable planning opportunities on the financial calendar.
If you haven’t already scheduled your review, now is the perfect time to get in touch with your financial adviser and accountant to ensure you’re making the most of every opportunity available to you.
If this article has inspired you to think about your unique situation and, more importantly, what you and your family are going through right now, please get in touch with your advice professional.
This information does not consider any person’s objectives, financial situation, or needs. Before making a decision, you should consider whether it is appropriate in light of your particular objectives, financial situation, or needs.
(Feedsy Exclusive)
