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New cash Isa deals are arriving thick and fast as providers jostle to offer headline-grabbing rates ahead of tax-year end.

These deals are great when you want to open and top up an Isa with new contributions. But those looking to transfer funds from another provider should make sure they read the small print, because the best rates often only apply to newer deposits.

What’s more, some providers that have launched attractive rates in recent weeks don’t accept transfers at all, leaving switchers out in the cold.

Despite top deals often being restricted to new contributions, it’s still worth checking the interest rate that you’re receiving in an existing cash Isa.

If it’s below 4 per cent – which is easily achievable with current deals – transferring is straightforward and can make a big difference to your savings.

We analyse the best cash Isa rates for transfers below, including both easy-access and fixed-rate accounts.

Top easy-access cash Isas for transfers

In recent years, easy-access cash Isa providers have been courting savers with attractive boosted interest rates on top of underlying variable rates.

The set bonus rate often lasts for a year and is usually only for new customers.

Some providers set restrictions around how much of your funds are eligible for the promotional rate. A few don’t accept transfers whatsoever, including Prosper, Tembo and Atom Bank.

And with boosted rates, you need to consider transferring again after the end of the bonus period, because the underlying rates aren’t always up to scratch. 

Isas have the advantage of being straightforward to transfer. But with some savers and investors amassing a small fortune within their accounts, offering the highest rates on both new contributions and transfers would prove costly for providers.

Moneybox: 4.27% on transfers but watch out for withdrawal penalties

The Moneybox cash Isa offers a good rate with no quirks around the process of actually transferring your Isa.

The 4.27 per cent rate includes a promotional 0.82 per cent boosted rate for 12 months, which applies to transfers too.

However your rate plummets to 0.75 per cent if you make more than three withdrawals in the year or when your balance drops below £500.

You should be sure you can meet the conditions for maintaining your rate if you plump for this option.

Moneybox also has a true open-access cash Isa with no withdrawal penalties, but this pays 4 per cent including a 0.75 per cent boost for 12 months.

Keep in mind that Moneybox doesn’t offer a flexible Isa, so if you withdraw then replace money it will reduce your Isa allowance.

> Find out more at Moneybox 

Hargreaves Lansdown*: ONLY if you haven’t maxed out this year’s allowance

The popular investing platform Hargreaves Lansdown has a cash Isa too. It works as a savings marketplace, with lots of different accounts available in one place.

This means you can switch between rates easily when better ones become available.

The top easy-access rate is 4.26 per cent offered through Vida Savings, matching the Moneybox rate. There’s no boosted rate to faff around with, but a curious quirk means you can’t transfer if you’ve maxed out this year’s allowance.

Hargreaves Lansdown doesn’t accept transfers directly to its cash Isa. Instead, you must transfer to its stocks and shares Isa first and then move uninvested cash to its cash Isa.

But you need to open the new cash Isa with at least £1 – so this isn’t possible if you’ve already maxed out your Isa elsewhere.

This is a true easy-access account with no restrictions on withdrawals, although it’s not a flexible Isa. This means your Isa allowance will reduce if you withdraw and replace money.

> Find out more at Hargreaves Lansdown* 

Plum*: 4.07% on transfers, 4.66% on new contributions

Plum made positive changes to its cash Isa last year after This is Money highlighted the issues bringing it down.

The provider will no longer penalise you by reducing your rate after three withdrawals.

It is paying 4.07 per cent on transfers including a bonus 1.53 per cent for a year. This is a fair amount less than the 4.66 per cent that new contributions will receive. Keep in mind that Plum’s Isa is not a flexible Isa. 

> Find out more at Plum*

Trading 212*: A solid but not table-topping rate on a good Isa

Big Plum rival Trading 212* is paying a high 4.68 per cent on current tax year contributions, including a 1.08 per cent boost for 12 months. But this will only help you if you switch cash paid in since last April. 

With the new tax year starting soon, the definition of ‘current’ tax year updates automatically and so the promotional rate soon won’t apply to many transfers.

Contributions from previous tax years earn the standard 3.6 per cent rate, which still beats most bank cash Isas and makes this a decent deal for transfers.

Trading 212 also applies no restrictions on withdrawing money and it’s a flexible Isa, so you can take out money and replace it in the same tax year without reducing your allowance.

Top fixed-rate cash Isas for transfers

Fixed-rate cash Isas provide the certainty of a set rate of interest for the length of the fix.

The good news is that you can find plenty of fixed-rate accounts that are friendly to switchers.

Vida Savings is offering a 1-year fixed-rate Isa at 4.37 per cent and accepts transfers.

For a 2-year fix, have a look at Furness BS, paying 4.45 per cent interest.