Some 10m state pension forecasts have been checked online since the launch of the government service in 2016.
Former pensions minister Sir Steve Webb said this showed the importance of including state pension data in the pensions dashboard.
The Department for Work and Pensions (DWP) has announced the milestone of the Check Your State Pension service, which it said had "quickly become the go-to way" for people to find out how much they could get in retirement, and when they could get it.
The online service can also help individuals work out whether they can improve their state pension, through voluntary national insurance contributions, or a workplace pension, for example, the DWP added.
Sir Steve, who is now director of policy at Royal London, said this was a "very significant" milestone and showed the huge level of public interest in their pension arrangements.
He said: "For that reason, it is vital that the proposed pension dashboard includes state pension information from the outset."
The government announced last week it would let the industry take lead on the dashboard project, but without a commitment to force providers to submit client data.
The plan behind the pension dashboard, which is due to launch in 2019, is to create the technology to allow savers to see all of their retirement pots in one place, giving them greater awareness of their assets and how to plan for their retirement.
According to media reports in July, secretary of state Esther McVey had made moves to kill off the project, saying the service should not be provided by the state.
But a DWP spokesperson said at the time the feasibility study was proceeding and that the reports amounted to no more than "speculation and rumour".
Sir Steve added the new state pension system – designed while he was pensions minister – was designed to be simpler, and most younger workers will simply get the new flat rate.
He said: "But the transition to the new system will take some years and it is important that older workers in particular use the online service to make sure that they know exactly what they are going to get."
Under the new system, introduced in 2016, pensioners receive approximately £150 a week or more if they have paid up 35 years of full-rate national insurance contributions, compared to the previous threshold of 30 years.