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Cash Isa providers are locked in a race to offer top interest rates ahead of tax–year end, with one provider launching an eye–catching rate of 6 per cent.

This rate from XTB* includes a fixed 2 per cent boost for three months, so to compare it over a full tax year you need to do the maths. Taking three months at 6 per cent and nine months at 4 per cent means your average rate over 12 months would be 4.5 per cent.

Meanwhile Plum* and Trading 212* have both inched up their headline rates, which are now as high as 4.68 per cent. This duo are regulars at the top of our best cash Isa savings tables and offer fixed 12–month boosts on top of their underlying rates.

For an even better rate, look at wealth management platform Prosper*. It has raised its headline rate from 4.5 per cent to 4.7 per cent since it launched its cash Isa last month. Keep in mind this also includes a 12–month boost.

And if you’re able to open a lifetime Isa and are willing to lock your money away, you can earn a show–stopping 5.05 per cent with Moneybox. Again, this includes a 12–month boost.

We examine the top deals in detail below. Keep in mind that all underlying rates are variable, which means providers can change them – usually in response to a base rate update. Boosted elements are usually fixed.

XTB – 6% (with 2% boost for three months)*

Investing platform XTB has launched a 6 per cent cash Isa, which includes a fixed 2 per cent boost that lasts 90 days from account opening.

You need to open the account by 30 April to take up the boost. The underlying rate is 4 per cent variable. At 0.25 per cent above the base rate, this is relatively high when compared with other options.

It’s a flexible Isa, which means you can withdraw money and replace it in the same tax year without reducing your Isa allowance.

There’s no minimum deposit, but a drawback is that XTB doesn’t currently accept transfers to its cash Isa.

You can only transfer to its stocks and shares Isa, which pays 4 per cent on uninvested cash but doesn’t come with the boost.

> Find out more at XTB* 

Prosper – 4.7% (with 1.92% boost for 12 months)*

Last month the upstart wealth management platform Prosper launched a cash Isa paying an attractive 4.5 per cent, but amid the new race to the top it’s climbed to 4.7 per cent.

We like that the account is a flexible Isa, with no penalties such as rate reductions for withdrawing money.

However, the underlying rate is relatively low at 2.78 per cent and there’s a high minimum deposit of £10,000 – plus transfers aren’t currently supported.

Still it could be a good option if you haven’t used your allowance yet. Prosper is also a low-cost investing platform the offers a Sipp free of account fees.

> Find out more at Prosper* 

Trading 212 – 4.68% (with 1.08% boost for 12 months)*

Trading 212 has one of our favourite cash Isas in terms of both interest rate and features. The investing platform has consistently offered a top rate, has a low minimum deposit of £1 and you can transfer previous accounts – although the boosted rate only applies to contributions made this tax year.

The underlying rate is high at 3.6 per cent – tracking 0.15 per cent below the base rate.

The account is a flexible Isa and has no penalties for withdrawing your money.

> Find out more at Trading 212* 

Plum – 4.66% (with 2.12% boost for 12 months)*

Plum is worth a look, especially if you’ve exhausted boosted rates for new customers elsewhere. It accepts transfers – although these earn 4.07 per cent, including a lower fixed boost of 1.53 per cent.

There’s a low minimum deposit of £1.

Late last year, Plum removed penalties, so it no longer punishes you by reducing your rate when you make more than three withdrawals or when your balance plummets.

This was after This is Money said that these features stopped it from being one of our favourites.

The main drawback with this account is that it’s not a flexible Isa.

> Find out more at Plum* 

Hargreaves Lansdown – 4.3% (no boost)*

This is a top account if you don’t want to bother with a boost, with a good rate of 4.3 per cent variable.

It’s Hargreaves Lansdown’s own cash Isa, provided in partnership with Shawbrook Bank and available through its savings platform.

There are some drawbacks – it's not a flexible Isa and you can’t transfer money directly to the account. Instead, you must transfer to Hargreaves Lansdown’s stocks and shares Isa first.

You only need £1 to get started, though.

> Find out more at Hargreaves Lansdown* 

Alternative to consider – Moneybox lifetime Isa (5.05%)

Moneybox’s regular cash Isa often features in our round ups, but its lifetime Isa is a top account that’s worth considering if you’re saving for a home deposit.

The rate has broken the 5 per cent barrier – it includes a fixed 2.25 per cent boost for 12 months.

You can save up to £4,000 a year into a lifetime Isa, with the Government topping up your contributions by 25 per cent – but you have to be aged 18–39 to open one.

You can only withdraw money when you buy a home or once you reach 60. You also need to watch out for the fact that the maximum purchase price of the property can’t exceed £450,000.

Keep in mind that the Government is consulting on replacing the lifetime Isa with a new product, but for now nothing is changing – read more about whether it’s still worth opening one.

> Find out more at Moneybox