If you've started putting away money for a first home or for your retirement, you might think you're doing the right thing.
But if your circumstances change, some savings accounts 'punish' their owners - and even leave them withdrawing less cash than they originally put in.
The taxman has managed to claim £9million of people's ISA savings over two years, a freedom of information request by Royal London has found.
As The Mirror reports , it all comes down to how Lifetime ISAs work.
Designed to encourage people to save for their futures, the lifetime ISA offers people a bonus of up to £1,000 a year added on top of whatever they pay in between the ages of 18 and 50.
To get the cash, you need to either put the money towards your first first home or keep hold of it until you are 60 to help fund your retirement.
What you might not realise is that is that if you take your money out for any other reason at all, you not only lose the extra cash the Government would have paid in, but they take a bite out of your original savings too.
Steve Webb, director of policy at Royal London, said: "A lifetime ISA can be attractive for those who are clear about their plans to put down a deposit on a house and who are confident that they won’t need the money for any other reason."
But, he warns, if there's any chance your circumstances might change, be careful, because you could actually end up walking away with LESS than you put in.
What do you lose?
It's all a little bit complicated, and easy to miss. The idea of the Lifetime ISA is that the Government will add 25% of whatever you pay in (with a maximum of £1,000). But they'll take that away if you don't spend it on a first home or withdraw after your 60th birthday.
Which all sounds reasonable.
Except the 25% they take away is 25% with the extra cash they've given you already added. So it's 25% of a bigger pot.
In pound terms - imagine you pay in £80. The Government then adds 25% to it - working out at £20.
That leaves £100 in the pot.
If you then withdraw that £100, but not for a house or retirement, the Government takes its 25% again - but this works out at £25 this time.
Which means, for every £80 you pay in you only get £75 back.
"It is hard to see why the Government should fine people whose only ‘crime’ was to put money aside in the hope of buying a home and then see their circumstances change," Webb said.
"The lifetime ISA would be a much attractive product if this penalty charge was abolished."
