The "Lifetime Isa", which has been available since April, is a new option for those who want to save up to buy their first home or build a retirement savings pot.
The Lifetime Isa effectively replaces the Help to Buy Isa, which was introduced in December 2015 to help those who wanted to buy their first property with a 25pc government boost on contributions of up to £200 a month.
Many experts say the Lifetime Isa is an improvement: the Government still pays a bonus of 25pc but on a more generous annual allowance of £4,000 a year. But there are some catches.
We've outlined everything you need to know about the new Lifetime Isa, including the companies that offer them, below.
Who can save into a Lifetime Isa and how much can they save?
You can open the account if you are aged 18 or over and less than 40. You can save up to £4,000 per year. The Government will then contribute £1 for every £4 – so £1,000 a year extra if you save the full £4,000.
Those who pay in the maximum amount between the ages of 18 and and 49 could see their savings boosted by £33,000.
Try our calculator to see how much you can make from a Lifetime Isa.
For the 2017-18 tax year the Government bonus will be paid at the end of the year but in subsequent years it will be added to the account monthly.
What happens when I want the money?
You can get hold of the money if you’re spending it on a first home (worth up to £450,000), for any reason once you’re over 60, or at any age if you're terminally ill.
If you need the money earlier for some other reason, for example if you lose your job, you will pay a 25pc charge on your total pot. This is intended to reclaim the government bonus, but it will also take a chunk of any interest or investment growth.
If you do need early access to your funds, you could actually end up with less than you put in.
For example, say you invest £100. The Government will give you a 25pc top-up, which will mean you have £125 in total. But if you need early access the 25pc exit penalty means you will end up with just £93.75. This is an effective 6.25pc tax on your savings.
Who will provide Lifetime Isas and what exactly do they offer?
Hargreaves Lansdown, The Share Centre, AJ Bell and Nutmeg were the first firms to offer an investment Lifetime Isa.
Moneybox, an investing app, is the latest provider to get involved.
Skipton Building Society is the only provider to offer a cash-only Lifetime Isa. The interest rate from Skipton has increased from 0.5pc to 0.75pc, which is less than many other Isas and savings accounts, but the 25pc Government boost cannot be beaten.
Skipton has recently announced a deadline of March 1 for savers with Help to Buy Isas to transfer their cash into its Lifetime Isa for this tax year - read here for more.
The offerings from the other providers are harder to compare.
Brokers Hargreaves Lansdown and AJ Bell both allow investments into a range of funds and shares. Hargreaves charges 0.45pc a year and AJ Bell charges 0.25pc.
Fund fees, which are additional to this, depend on the investment choices you make. You must invest at least £25 a month or deposit a £100 lump sum to open either account.
AJ Bell and Hargreaves Lansdown permit savers to hold their money in cash although AJ Bell doesn't pay interest on balances under £50,000. Those with more will earn just 0.05pc - the same rate offered by Hargreaves Lansdown on cash savings above £5,000.
Both charge high transfer fees of £25 per holding if you want to move to a new provider.
The Share Centre and Nutmeg have more restricted offerings.
The Share Centre is limited to three funds designed for cautious, moderate and adventurous investors. The only fees you pay are fund charges of between 2pc and 2.21pc, although these are on the high side.
The Share Centre said it was working to offer a wider range of investments for Lifetime Isa savers. It also charges £25 to transfer shares to another provider.
Nutmeg charges 0.75pc on investments of up to £100,000 for its fully managed portfolio range, and 0.45pc for its "fixed allocation" portfolios. Additional fund charges also apply of 0.19pc and 0.17pc respectively, on average.
Moneybox charges £1 a month to investors - although it's free for the first three months - and 0.45pc of the value of your investments each year. It offers three tracker funds from asset managers Henderson, BlackRock and Vanguard that track the global stock market, property and cash.
If you decide to transfer your holdings to another provider, you'll be charged £25 per fund.
What sort of investments can I hold in my Lifetime Isa?
A Lifetime Isa will be able to contain any mixture of investments that qualify for either cash or stocks and shares Isas: cash, bonds, shares and investment funds that invest in shares or bonds.
Because this is a separate Isa type, an individual can still have a cash Isa, stocks and shares Isa and/or an Innovative Finance ("peer-to-peer") Isa alongside a Lifetime Isa.
What happens when I turn 40?
If you already have a Lifetime Isa you will be able to continue saving into it and still get the Government bonus up to age 50.
If you're over 40? Tough - you cannot start a Lifetime Isa and will have to save into a pension or a conventional Isa instead.
You cannot make contributions into the Lisa beyond the age of 50, although you cannot access the money until you turn 60.
How do I know whether future governments will stick to the system?
You don’t. That’s another drawback, although it applies to any tax perk.
I’m already saving into a Help to buy Isa. What will happen to it?
You can transfer funds saved into your Help to Buy Isa into a Lifetime Isa before April 5 2017 without it affecting your annual allowance.
The Government bonus will be applied to the combined sums, as seen in the example below.
If an individual transferred £4,200 from a Help to Buy Isa into a Lifetime Isa, and contributed the £4,000 annual Lifetime Isa allowance this tax year too, they would receive a 25pc bonus on £8,200 in the first year, amounting to £2,050, taking their total to £10,250.
Any Help to Buy Isa transfers after the first year will count towards the annual £4,000 Lifetime Isa contribution limit.
By November 2019 you’ll no longer be able to open a Help to Buy Isa.