Britons lose £40 a year typically through informal cash loans handed out to friends, family members and work colleagues who never pay them back, a survey has found.
Those handing out the money will typically start trying to chase it up when the debt reaches just £4, according to the research from Nationwide Paym.
Four-fifths (80%) of people surveyed said they start to chase up cash owed to them by a friend, relative or work colleague before it reaches £6.
And one in eight (12%) people would pursue a debt no matter how small it was.
With people being left £40 a year out of pocket typically, they could end up well over £2,000 down over the course of a lifetime of handing out small cash loans to friends, family and work colleagues that they never get back.
People in Northern Ireland would hold off chasing a loan until it reached £5.75 on average - while in the West Midlands people would start pursuing a debt when it reached £3.16 typically.
Younger people tend to be hardest hit by unpaid debts, the research suggests, with 18 to 24-year-olds losing £74 a year on average in money they loan out that does not get paid back.
Half (50%) of those surveyed feel small loans made in this way should be paid back in under a week - while 1% believe it is acceptable to never return borrowed money, the survey of 2,000 people found.
Nationwide Building Society is one of many banks and building societies taking part in mobile payments service Paym, which enables people to send and receive cash using just a mobile phone number, rather than needing account numbers and sort codes.
Paym was introduced to Nationwide's customers last year and £3.3 million has been sent so far using the service, with the average payment being £33.36.
Here are the average amounts at which people across the UK will start chasing a debt, according to Nationwide Paym, followed by the average amounts they lose each year in unpaid loans made to family members, friends and work colleagues:
:: East Anglia, £4.37, £35.64
:: East Midlands, £3.55, £34.68
:: London, £4.40, £41.40
:: North East, £4.63, £50.88
:: North West, £4.05, £51.00
:: Northern Ireland, £5.75, £41.16
:: Scotland, £4.65, £39.96
:: South East, £3.97, £34.68
:: South West, £3.72, £33.00
:: Wales, £3.36, £35.52
:: West Midlands, £3.16, £33.48
:: Yorkshire and the Humber, £4.31, £44.04