Nearly a third of people (31%) have had difficulty in finding a family member's assets bequeathed to them in a will, and they could be missing out on £9,700 each on average.
The research by website willsandassets.co.uk found that some £175 million could be going unclaimed.
Tracking down assets can be an expensive business. Some 39% of people who have lost loved ones spent an average of £2,250 on solicitors' fees to complete the task following a death in the family, the research found.
More generally, 49% of people have wills but there are big differences across the regions. Just 36% of people in the North East have a will, compared to 55% in the South East.
Stephen Foden of Willsandassets.co.uk said: "No one wants to think about what will happen when they die but failing to do so can leave loved ones with significant problems and stress at an already very tough time."
"With more than 175,000 people a year struggling to sort out loved ones' finances there is clearly a need for better planning."
It's also worth noting that the rules of intestacy - what happens to an estate when someone dies without a will - changed in England and Wales at the start of October. They are as follow:
- For a married person with no children – their spouse or civil partner will inherit everything. Previously, they would have shared the estate with the deceased's surviving parents and siblings.
- Married person with children – their spouse will inherit the Statutory Legacy of up to £250,000 (as they did previously) but they will now also inherit the deceased's personal belongings and half of their estate automatically. The children then inherit the remaining half share of the estate on trust until they turn 18. Under the old rules, the spouse would only receive the income of the half share of the estate, which would pass on to the children upon their own death.