Parents still want to help their kids onto the housing ladder, but the average contribution has fallen 17% to £18,000 from £21,600 in 2017.
Despite this, the Bank of Mum and Dad remains a major force in the UK housing market, according to the study by Legal & General (L&G).
Some 27% of buyers will receive help from friends and family this year, up from 25% in 2017.
And parents are expected to help 316,600 loved ones buy a home, up from 298,000 last year.
The value of parental-supported property purchases in 2018 is set to rise to £81.7bn, a £4.2bn or 5% increase since 2016.
Nigel Wilson, group chief executive at Legal & General, said: “The fact that in 2018, 1 in 4 housing transactions in the UK will be dependent on the Bank of Mum and Dad, while hard-pressed parents are finding it more difficult to provide the funds to help their family with deposits, will further exacerbate the UK’s housing crisis.
“We need to build more homes for the young, old and families alike – more quickly and cost effectively.”
The research found that Bank of Mum and Dad contributions are highest in London (£31,000 per transaction on average) and lowest in Scotland (£11,000). More buyers in London receive parental help than in any other region.
Under 35s are most likely to receive help from their parents, but even buyers aged between 45 and 55 are relying on mum and dad, with one in five receiving parental assistance.
Equity release has increased slightly as a source of funding for a loved one’s home purchase, from 3% to 4%.