The 2011/12 tax year starts today, meaning everyone gets a new tax-free cash Isa allowance. But don't delay using it as it every day you stall you're losing interest.

Every UK citizen over 16 years old can now deposit a maximum of £5,340 into a cash Isa during the current financial year, an increase from last year's £5,100 allowance (see the Top Cash Isas Guide).

But last year's pot is closed so if you missed yesterday's deadline it's gone forever.

Consumers should consider cash Isas as their first port of call when saving, as they are normal accounts where the interest is always tax free, unlike a conventional savings vehicle.

The top easy access Isa rate from the AA pays 3.35% compared to the top standard easy access deal from Santander that pays 3%. After tax, that's 2.4% for a basic rate taxpayer (see the Top Savings Accounts guide).

On a £5,340 balance you'd earn £179 over a year in the Isa compared to £128 in the standard account – £51 more.

Even if you've opened a cash Isa in previous tax years, you can now do it again. Alternatively, if the account allows, you can top up last year's balance with the new maximum.

But make sure you're not languishing on a pitiful rate (see best buys below).

The restrictions with cash Isas are that you can only save up to the £5,340 limit in this tax year, you can only open one to deposit new money in per tax year and you must be 16 or over.

You can open another account to transfer money from old Isas.

The top new easy-access Isas

Our top-pick easy-access Isa is Santander's Flexible Isa (issue 3), which pays 3.3%, although some existing customers get 3.5%. It tracks base rate for a year so if the rate rises so too will the return on your savings.

Barclays's 3.25% Golden Isa is the next best base rate-tracking product. However, the AA's Isa pays a higher 3.35% but it doesn't guarantee to track base rate.

The current top easy-access Isa that allows transfers from old Isas is Halifax's Isa Direct Reward which pays 3%, or 3.2% to some existing customers. It does not guarantee to track base rate (see the Top ISA Transfers guide).

All the top easy access savings products come with bonuses that usually last a year so ensure you ditch and switch when your deal expires.

The top new fixed Isas

If you're prepared to lock your cash away for a set time you get a guaranteed rate with a fixed Isa.

Be warned that you face heavy withdrawal penalties for taking the money early. And while the initial rates are often higher than easy access deals you will not benefit if base rate rises.

The current top two-year fixed cash Isa is from Santander at 3.7%, with a minimum deposit of £500. For five years, the top option is Birmingham Midshires at 5%, again with a minimum deposit of £500.

Further reading/Key links

Top deals: Cash Isas, Isa Transfers, Full Isa Guide