The Department for Work and Pensions released the figures and explained that this compared to 860,000 State Pension forecasts issued in the previous 12 month period.
Eighty per cent of the forecasts requested were viewed online.
Pensions Minister Richard Harrington said: “Not only is the new State Pension system simpler, but it’s now easier than ever before for people to find out what they can expect to receive when they retire.
“Just as we’ve seen more people using online banking, so too are people welcoming the opportunity to take more control over their State Pension.
I want to encourage everyone to use this online service to help them make informed decisions about their retirement, and I’m delighted that so many savvy savers are already doing this.
“Check your State Pension’ was available to the public on 11 February. In that month it received 18,000 visits, but by September 2016 this figure had risen significantly to 343,000.
“Anyone of working age can use the service to access their State Pension forecast. It provides a personalised estimate of what they may receive and highlights any gaps in National Insurance contributions, and whether these can be filled with voluntary contributions.”
User satisfaction with the online service is around 90%, the DWP reported.