An even smaller proportion of respondents surveyed by wealth management and investment group Sanlam maximised their pension contributions.
Only 20% had made full use of their annual £40,000 tax-free pension allowance.
Those with higher assets were more likely to make full use of their saving allowances.
Only a third of Brits surveyed with investable assets of between £50k-£100k maximised their ISA contributions, compared to 71% of those with over £1m.
Only 13% of respondents with between £50k-£100k of investable assets said they maxed out their pension contributions against 43% of those with more than £1m.
Those who maximised their ISA contributions were more likely to be receiving financial advice. Over half (59%) who said they used the full allowance said they regularly consulted a financial adviser.
The survey was conducted for Sanlam by Ad Lucum for Technical Connection in February.