The RCN analysis shows junior nursing staff have been the worst hit, with Band 5s (21%) seeing the biggest erosion of their wages.
It comes as tens of thousands of nursing staff across England, Wales and Northern Ireland continue to vote in the RCN's consultation on this year's 3.6% pay award.
The new analysis shows that had pay kept up with RPI – the most accurate measure for the cost of living - since 2010, the starting salary for a registered nurse would be nearly £40,000 a year.
For band 5 nurses, sustained low and below inflation awards between 2010 and 2025 account to a cumulative loss of earnings of £70,000.
The RCN says addressing ‘collapsing wages' for those at the start of their careers must be a priority for the government, especially if it wants to boost recruitment into the profession and deliver the government's 10-Year Health Plan.
Even by the Government's favoured CPI measure, which ignores the exorbitant cost of housing, the analysis shows that this year's award is worth just an extra £5 a month for a new nurse, equivalent to the cost of a supermarket meal deal.
The financial picture is worse still for lower-paid nursing support staff at band 3, for whom the award is worth less than £4.38 extra a month.
Executive director for RCN England, Patricia Marquis, said: 'This award is derisory. It does nothing to reverse the trend of collapsing wages, especially for nurses at the start of their careers, and even by the government's own calculations barely covers the cost of a sandwich and a drink. Nursing staff are tired of playing constant financial catch-up, often struggling to pay rent or get on the housing ladder.
'Nursing is an incredible profession, but we are weighted to the bottom of the NHS pay scales and received one of the lowest awards this year, a situation which is deepening the workforce crisis and impacting patient care. Attracting and keeping talented people should be the government's priority, but that requires them to do better on nursing pay.
'Our members are voting in their tens of thousands and making their voices heard on this pay award. Ministers must realise that the only sensible choice left to them to negotiate directly with the largest health care workforce. It is time to both deliver better pay and pay modernisation for nursing staff.'