The eleven days
the taxman never gave back
In Britain, Wednesday 2 September 1752 was followed by Thursday the 14th. Eleven days left the calendar in order to close the Julian gap. They left neither the leases, nor the annuities, nor the Treasury's books: which is why the British tax year still ends on 5 April, and not on 25 March.
A calendar corrected, debts left intact
The Calendar (New Style) Act, given royal assent on 22 May 1751 and in force from 1 January 1752, settled two delays at once. It moved the start of the civil year from 25 March, Lady Day, to 1 January; and it brought the kingdom into line with the Gregorian calendar by deleting eleven dates from September 1752. Legend has it that a crowd demanded its eleven days back. No contemporary source attests to it: the phrase comes from a banner painted by Hogarth in 1755, where it serves as an election slogan.
The Act took care, however, to subtract nothing from obligations. Its sixth section provided that rents, annuities, interest and leases did not fall due eleven days earlier: every payment date was deferred by the same span, as though the calendar had not moved. The legislator corrected the measuring instrument without touching the quantity measured. A tenant still owed a full year of rent, a creditor still received twelve months of interest.
The Treasury applied the rule to itself. The fiscal year, which ran to 25 March, would have lost eleven days of receipts: it was extended by as much, and the following year of assessment opened on 5 April 1753. A further one-day shift, most often traced to the year 1800, a leap year under the Julian calendar but not under the Gregorian one, moved the date to 6 April. It has not moved since.
Contract time is not calendar time
The episode isolates a distinction easily forgotten when all goes well: a date is a convention, a debt is a duration. Every reform of the unit raises the same question, and legislators have answered it ever since with a continuity-of-contract clause: the changeover to the euro in 1999, monetary redenominations, the replacement of Libor by rates computed on another basis, together with an adjustment meant to wrong neither lender nor borrower.
Then comes the less noble lesson: an accounting decision taken so as not to lose eleven days of receipts still governs the calendar of tens of millions of taxpayers. In September 2021 the Office of Tax Simplification examined moving that year end to 31 March or to 31 December. Its findings acknowledge the benefits of a date aligned with a month or with the calendar year, and the considerable cost of the change. Nothing has been decided.
A calendar can be corrected by a stroke of law; a due date never can.