Skipton Building Society has become the first Isa provider to outline its 'New ISA' (Nisa).
Customers will be able to make use of their full NISA allowance of £15,000 in July, even if they lock into a fixed-rate cash Isa or Junior Isa (Jisa) earlier in the 2014/15 tax year.
Between 6 April and the end of June savers can deposit the maximum cash Isa allowance of £5,940 into a Skipton's Fixed Rate ISA (its 1 Year Fixed Rate Cash ISA to 15 April 2015 currently pays 1.6% for the annual interest option or 1.59% for the monthly option). Then from 1 July when existing cash and stocks and shares ISAs are merged to become Nisas, customers can top up to the new £15,000 subscription limit for the rest of the tax year.
They will have to top up within the month of July to secure the fixed-rate the rest of their cash Isa deposit enjoys.
All Skipton easy-access Isa customers who deposit money before the introduction of NISAs will also be informed of the increased limit they can take advantage of from July.
Similarly, Jisa savers will be able to deposit up to £3,840 between 6 April and the end of June before topping up to increased allowance of £4,000 from 1 July. Skipton's current JISA pays 3.02%.
Skipton's head of products, Kris Brewster, said: "We have long campaigned on behalf of our customers for more simplification and fairness in tax-free savings. We welcomed this, the first budget to really address their plight in this historically low interest rate environment."
He added: "In what is usually unheard of in fixed-rate accounts, savers in Skipton's Fixed Rate ISAs for the 2014/15 tax year will be able to top up throughout the whole of July up to the new maximum Nisa limit."