A study found 175,000 people a year struggle to track down all the assets their family members have decided to hand down to them. On average these missed assets were believed to total £9,700.
But 12% of those who believe money went missing think it could be £20,000 or more.
The research also revealed that tracking down the assets can be expensive – 39% of those who have lost loved ones in the past 10 years have spent an average £2,250 on solicitors and other advisers after a death.
Part of the problem is people failing to draw up wills – just 49% have wills, rising to 79% among those aged 65-plus. But only 36% of those who have wills have updated them within the last two years and that only rises to 37% for those aged 65-plus.

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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 and our service provides a single secure place to store wills and to detail what financial assets there are and how they can be found."
Across the country people in the North East are the least likely to have wills – just 36% - while those in the South East are the most likely with 55% having wills. However people in Wales with wills are most likely to have updated them in the past two years.