The best cash Isas for the new 2021-22 tax year

The new 2021-22 tax year began on 6 April, meaning all UK citizens have a brand new £20,000 tax-free Isa allowance to use by 5 April 2022.

However, with strict rules and average Isa rates continuing to reach new lows (as they have done for the past few months), it can be hard to know where to start - but it's always important to make sure your savings are receiving as competitive a rate as possible.

Here, Which? reveals the cash Isas offering the top rates, how to transfer your existing Isa savings and how much you're allowed to save.

Best cash Isa rates for 2021-22

The table below shows the top rates for fixed-term and instant-access cash Isas, by order of term.

_{Source: Moneyfacts. Correct as of 7 April 2021, but rates are subject to change.}

As the table shows, most of the top rates are offered by the same provider at the moment - Punjab National Bank.

There's currently no difference between the top-rate instant-access account and the top one-year fixed-term account, which is very unusual. While it does make the idea of fixing for a year look a little pointless, note that instant-access account rates can change at any time, so you could find yourself earning much less interest in the future, whereas at least it's guaranteed with a fixed-term account.

As CPI inflation fell to 0.4% in February 2021, currently all of these accounts do exceed this rate - but only just. If your savings fail to grow at the same rate as inflation your cash will lose value in real terms.

Finally, note that all of the top-rate accounts here, bar the instant-access account, require a minimum initial deposit of at least £1,000, so you'll need to make sure you can both afford that sum when you first open the account and can do without it for the full term.

• Find out more:how to find the best cash Isa

How much can you save into an Isa in 2021-22?

The overall Isa allowance for 2021-22 is £20,000, which is the same as it was last year.

This is the overall allowance you can deposit into any kind of Isa, whether that's all into a cash Isa, or split among a cash Isa, stocks and shares Isa, innovative finance Isa and a lifetime Isa - note that you can only deposit up to £4,000 into a lifetime Isa in each tax year.

You can only save into one of each type of Isa in each tax year; if you pay into an existing Help to Buy Isa (now closed to new customers) in 2021-22, you won't be able to pay into any other cash Isas in this tax year, as it counts as your cash Isa option. These accounts only accept deposits of up to £200 per month.

However, you can pay into a cash lifetime Isa and a cash Isa within the same tax year, as a lifetime Isa is counted as a different type of Isa.

• Find out more:cash Isa rules and allowances

When is the best time in the tax year to save?

While the end of the tax year is often referred to as 'Isa season' - a time when many savers hurry to deposit what's left of their remaining Isa allowance before it renews each 6 April - it's not the best time to make your deposits.

In fact, the best time to maximise your Isa savings is now, at the start of the tax year. There are several reasons for this:

• You'll make the most of compound interest: while it may sound obvious, the longer your cash is receiving interest, the more it will grow. By depositing as much of your Isa allowance as possible at the start of the tax year into an account that pays monthly interest, your savings will build up month on month, even if you don't make any further deposits.
• You're more likely to save on tax: Isas are a way of avoiding paying tax on savings interest, so if you deposit your savings into an Isa at the start of the tax year, you won't have any savings interest to add to your 2021-22 income.
• You'll avoid further rate cuts: according to data from Moneyfacts, average rates for instant-access cash Isas, one-year fixed-rate cash Isas and longer-term fixed-rate cash Isas (ie. those with terms of 18 months or more) have reached record lows every month since October 2020, and there's nothing to suggest they've finished falling. With that in mind, getting a cash Isa with the most competitive rate possible now might shield you from future interest drops.

How to transfer existing Isa savings

If you've been incredibly quick off the mark and already paid into a cash Isa in this tax year, but have spotted a better rate elsewhere, all is not lost.

You may be able to take advantage of the better rate by transferring your Isa savings to the new account.

If you've committed to a fixed-term cash Isa, this may not be allowed, or you may have to pay an interest penalty.

To make a transfer, you'll need to fill out an Isa request form with the new provider, which will then contact your existing Isa provider and organise the transfer - don't be tempted to withdraw the money and deposit it yourself; not only will this break the Isa rule of only paying into one account in each tax year, but your cash will also lose its tax-free status if it's removed from the Isa 'wrapper'.

If you're transferring between cash Isas, the process should take no longer than 15 working days. It's also possible to transfer between different types of Isas using the same process, but the timeframes can differ - and, if you transfer out from a lifetime Isa into another type of Isa you'll face the lifetime Isa withdrawal penalty.

Be mindful that not all Isas accept transfers, so make sure you check the account's terms beforehand.

• Find out more:how to transfer your cash Isa

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