Around four in ten people who deal with administering a loved one's estate without using an adviser spend more than two days on the task, according to a survey.
The Office of Tax Simplification (OTS) found 38% of 3,000 respondents said it had taken them more than 50 hours to complete, with some spending more than 100 hours.
Estate administration is the process of handling a person's tax and legal affairs after they have died, while tax is deducted on the value of the estate before being distributed to beneficiaries.
Despite inheritance tax being levied on only 5% of estates in the UK, inheritance tax returns still need to be filed with HMRC on around half of all deaths.
Completing a return includes obtaining formal documents, calculating the value of their estate, working out and paying taxes and obtaining a grant of probate.
For 31% of those polled by the OTS, the process took between 21 and 50 hours.
Among the most time-consuming processes for most respondents were understanding and completing the relevant forms (38%) and obtaining probate (24%).
Meanwhile, only 11% of people said they had found the process simple and user-friendly, prompting calls for the inheritance tax system to be digitally overhauled.
Paul Morton, tax director at the OTS, said:
"Technology should be deployed to provide a digital solution to transform the experience of those dealing with the tax on a day-to-day basis."
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