Droves of retirees are risking outliving their pension savings as they are vastly underestimating their life expectancy, a major provider warns.

Almost one in three retirees in their 70s have already outlived the age they expected to reach when they were in their 50s, according to financial firm Aviva and charity Age UK.

This means that they may not have enough funds to sustain their spending for the rest of their life.

Plus, more than three in four people don't believe they will live beyond 85 prompting fears that many are under saving for their retirement.

But in reality, they will live longer than expected. One in four men who are currently 70 are expected to reach 92 , while one in ten could reach 96. 

And for women the odds are higher - 5 per cent of 70 year olds have a chance of reaching 100, according to the Office for National Statistics.

And these odds are only likely to increase with time as modern medicine continually develops.

It means that savers will have to retire later - or set aside more money.

This comes as financial planners say they are increasingly planning for retirees to live to 100 to ensure they are not short of funds in their later years.

If you retire at 57 - the age which you will be able to access your private pensions from 2057 - and live until 100 then you'll have to build funds to sustain spending for almost half of your life.

It is worthwhile getting financial advice when you are planning how to pace your retirement savings so you don't run out pf money should you reach 100.

A financial adviser can come up with a plan on how much you should be spending to have your desired lifestyle but also to make sure your savings last for an appropriate amount of time through a specialised tool called cash flow forecasting.

If you don't get financial advice you may end up spending your pots quicker than you should or living frugally when you don't need to.

Emma Douglas, wealth policy director at Aviva, says: 'We don't have a crystal ball to tell us how long we're going to live - and our report findings highlight that today's mid-retirees could be making important financial decisions based on incorrect assumptions about life expectancy.

'It can be tricky to get the balance right for a sustainable retirement income - living for now, while also saving enough for later life.

'A step in the right direction is to ensure you are fully informed. Having the right conversations with the right people, and at the right time, will help you to get ready for a retirement that might be much longer than planned.'

Pension tax relief can really lighten the savings load for your decades-long retirement. You may get this automatically if you are paying into a workplace pension via salary sacrifice.

But if you are paying into a personal pension such as a self-invested personal pension, remember to claim back tax relief if you are a higher or additional rate taxpayer.

If you are a basic-rate taxpayer, every 80p you save into a pension is topped up to £1 by the taxman.

Higher and additional-rate taxpayers need only put in 60p or 55p respectively for it to be topped up to £1.

A financial adviser will also be able to help you with how to take your pension. Perhaps drawdown is better for you, an annuity or a mix of both.

Annuities could give you peace of mind, Aviva says, as they guarantee regular income in later life. It's especially true if they are inflation linked but these do tend to be more expensive as they will be more lucrative than a fixed-rate annuity.

You can use an annuity calculator to see an estimate of what your pot could buy.