18 February 2026
ISA allowances and the habit of leaving cash idle
Unused ISA capacity is common among households who keep large current-account balances for comfort. Comfort has a cost when inflation outruns deposit rates.
We meet many Castle Murphy households who keep eighteen to thirty months of spending in easy-access accounts because a parent once lost sleep during a rate rise. That caution is understandable. Leaving the entire buffer unexamined year after year is not.
A practical approach starts by naming the true emergency reserve — often three to six months of essential costs — and parking it in an easy-access account you will actually use. Amounts above that line can be staged into a Cash ISA or stocks-and-shares ISA according to time horizon and temperament.
The annual ISA allowance resets each tax year. Unused capacity does not roll forward. Couples can coordinate who uses which allowance, especially where one partner has more taxable interest or dividend income outside wrappers.
We do not treat every pound above the emergency reserve as fair game for equities. Known costs inside three years — a kitchen renovation, a wedding contribution, a university deposit — usually stay in cash or short-dated holdings. Money with a seven-year or longer horizon can tolerate market movement if the household sleep test still passes.
Bring a recent bank summary and last year's ISA statements to a Comprehensive Wealth Review if you suspect idle cash has grown without a plan. The recommendation is often a staged transfer calendar, not a single dramatic move.