# invest.isa-allowance

How much of each ISA subscription limit has been used in a UK tax year and how
much is left: the overall adult limit, the Lifetime ISA limit inside it, the
cash ISA limit inside it (from 2027/28, for savers under 65), and the Junior
ISA limit, which is the child's own allowance.

## Why it is shaped this way

- **Limits inside limits.** A Lifetime ISA's £4,000, and from 2027/28 an
  under-65's £12,000 of cash, count towards the £20,000. So what is left of
  them is also capped by what is left overall: £18,000 in a stocks and shares
  ISA leaves £2,000 of Lifetime ISA room, not £4,000.
- **Junior ISA is separate.** It is the child's allowance, counted on its own
  and never against the adult's. Pass one child's subscriptions (or leave
  them out).
- **`exceeded`, not an error.** An over-subscription is a fact to report
  (HMRC repairs or voids the excess), so the function answers with the flags
  set rather than throwing.
- **Each tax year is its own row** in `data/isa-limits.json`, so the label and
  the 6 April to 5 April bounds come from the data and a year the data does
  not cover (before 2017/18, after 2027/28) is refused rather than guessed.

## The 2027/28 cash limit

From 6 April 2027 the government has announced a cash ISA limit of £12,000
for savers under 65, inside an unchanged £20,000, with savers 65 or over able
to put the full £20,000 in cash "from the start of the tax year in which an
individual turns 65". Here that means: a saver whose 65th birthday falls on
or before 5 April at the end of the tax year has no separate cash limit
(`cash` is null); anyone younger has the £12,000 limit, and `dateOfBirth` is
then required. A 29 February birthday is compared as the string
"YYYY-02-29", which sorts correctly.

At 2026-09-23 this is announced policy (policy paper published
17 September 2026) with the amending ISA Regulations still in draft. The row
is marked so in its note; if the final regulations differ, publish a new
version with the corrected row.

## Limits

| Tax years | Overall | Lifetime ISA | Junior ISA | Cash, under 65 |
|---|---|---|---|---|
| 2017/18 | £20,000 | £4,000 | £4,128 | none |
| 2018/19 | £20,000 | £4,000 | £4,260 | none |
| 2019/20 | £20,000 | £4,000 | £4,368 | none |
| 2020/21 to 2026/27 | £20,000 | £4,000 | £9,000 | none |
| 2027/28 | £20,000 | £4,000 | £9,000 | £12,000 |

## Out of scope

Lifetime ISA age rules (open under 40, pay in until 50) and the government
bonus; whether a cash Lifetime ISA counts towards the cash limit (it is not
counted as cash here); transfers between ISAs, which are not subscriptions;
flexible ISA withdrawals and replacements; the 2027 anti-circumvention rules.

## Sources

Read on 2026-09-23:

- GOV.UK, "Individual Savings Accounts (ISAs): How ISAs work" (£20,000 a year;
  Lifetime ISA £4,000 a year, inside it):
  https://www.gov.uk/individual-savings-accounts/how-isas-work
- GOV.UK, "Junior Individual Savings Accounts (ISA)" (£9,000 in 2026/27):
  https://www.gov.uk/junior-individual-savings-accounts
- HMRC, "Annual savings statistics: background and methodology" (Tables of
  adult and Junior ISA subscription limits by tax year, 2008/09 to 2026/27):
  https://www.gov.uk/government/statistics/annual-savings-statistics-2026/annual-savings-statistics-background-and-methodology
- HMRC policy paper, "Cash Individual Savings Account (ISA) limit reduction",
  published 17 September 2026:
  https://www.gov.uk/government/publications/reduction-in-the-cash-individual-savings-account-isa-limit/cash-individual-savings-account-isa-limit-reduction
- "ISA reform 2027: anti-circumvention rules factsheet" (the age 65 test):
  https://www.gov.uk/government/publications/fiscal-events-2026-factsheets/isa-reform-2027-anti-circumvention-rules-factsheet

1.0.1 fixes Python accepting a trailing newline or non-ASCII digits in taxYearDate, dateOfBirth and subscription dates; adds tests.