The number of members to have ever used NEST rose by 28% over the 2018/19 fiscal year to 31 March, according to its research arm, NEST Insight.
In a report published 16 October in partnership with Vanguard, the master trust noted that while the majority of members that joined NEST over the year were auto-enrolled, over 250,000 (8%) of people actively chose to participate in the master trust.
The document, which is the second of its kind titled How the UK Saves, showed many of these members were on "very low incomes" with 17% earning under the AE threshold of £10,000.
When last year's report was published in July 2018, NEST's membership stood at around 6.5 million. As at the end of March, the master trust managed £5.7bn on behalf of a total of nearly eight million employees, and 826,000 employers. The average NEST member is 37 years old, and earns £18,563.
The report showed opt-out rates under ongoing enrolment rested at 7%, up just one percentage point from last year, despite the increase in minimum AE contributions to a total of 5% from 3% in April last year.
Contributions rose again to a total of 8% with 5% minimum employee contributions this year, but the data in the report does not reflect the last increase.
As at 31 March 2019, 84% of employers had enrolled workers at the statutory minimum, while a further 13% of employers had enrolled members with higher worker and/or employer contributions.
Combined employer and employee contributions above 8% in the 2018/19 fiscal year increased to 5% of its membership from 3% in 2017/18, while the number of total contributions of 6% to 8% increased from 2% to 8%.
Since the master trust launched in 2011, around a quarter of members had registered to their online account by the end of March. From January to June 2019, mobile and tablet devices became the dominant channel for member digital interaction with the master trust, at 54%. This was an increase from 50% last year, and 31% in 2015.
NEST Insight assistant director Matthew Blakstad said the second annual report paints a "striking picture" of the rapid adoption of workplace pensions.
He said: "Looking back to October 2012, we see that NEST had just 2,000 members enrolled by 175 employers, and minimal assets under management."
He added the increase in its membership "represents a huge change to the long-term financial wellbeing of people in the UK".
Blakstad concluded: "That makes it all the more important to monitor and understand the experience of auto enrolled savers. We look forward to tracking the evolution of workplace pensions through future reports."
The publication of the report follows a supplement version last month which revealed its male and female members exhibit equal savings behaviour.
Nonetheless, it showed its female membership were three times more likely to be under the AE threshold.
Speaking at the Pensions and Lifetime Savings Association's annual conference on 16 October, Vanguard senior research analyst Cynthia Pagliaro said: "We have done this research with a goal of trying to help inform policy makers and employers on the advocacy of defined contribution systems."
She added: "As a researcher I look at member engagement of the holy grail of investment behaviour. It's such a tough nut to crack. But trying to find ways is very challenging. So what we wanted to do is set a bassline by looking at member behaviour.
"Over time I expect to see engagement improve a little bit because we have studies that show as account balances grow, engagement increases. When the balances start to grow people love to look at their money."
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