Around 35% of over 50s have not written a will, according to research that coincides with Will Aid month.
The survey from RIAS found confusion about what happens to the estates of those who die intestate.
Of those surveyed 52% believed their estate would go to their spouse, which is true in most case, while 27% believed it would go to their next of kin.
There were regional variations with 44% of Londoners over 50 without a will while in the East Midlands 75% of over 50s had one in place.
Will aid month sees solicitors write wills in exchange for a donation to charity, and since its founding in 1988 has raised over £15m for nine charities and helped thousands write their wills.
Estates without a will in place can be subjected to higher taxes and part of the inheritance can be claimed by the government through the bona vacantia law, which last year provided the government with £40.2m of income, a 300% increase on the year before.
An awareness campaign, Plan If, was recently launched to encourage parents to prepare wills, protection policies and other documents in case of their death.
Peter Corfield, managing director at RIAS said: "It's clear from these findings that making a will is still a bit of a stumbling block for a lot of people over the age of 50.
"People with busy lives might say they don't have the time, whilst some people may not want to face the prospect of writing one up as they could see it as a real sign of getting older.
"This doesn't take away from the fact that getting a will is essential to make sure that should the unexpected happen, your family and friends receive the best support. If people don't have a will in place then your money, property and possessions will be shared out according to the law instead of your wishes. This can mean your estate passes to someone you hadn't intended - or that someone you want to pass things on to ends up with nothing."
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