The funded status of the 100 largest corporate defined benefit pension plans improved by $318 billion during 2013 as measured by the Milliman 100 Pension Funding Index (PFI). The year ended on an optimistic note as the index captured four consecutive months of funded status gains starting with September. Historically low interest rates were the dominant factor in 2012, but interest rates have since rebounded in 2013, increasing 87 basis points for the year and leading to large liability declines. Higher-than-expected investment returns added to the funded status improvement, as monthly returns were greater than expected in nine out of 12 months during 2013. Many plan sponsors will now have their sights set on attaining fully funded status for their plans in 2014.