The NISA Investment Advisors Pension Surplus Risk index rose 70 basis points in June to 10.6%.
The index is a forward-looking estimate of the funded status volatility of the 100 largest U.S. corporate defined benefit pension plans.
According to NISA, the index level represents a one standard deviation change in funded status over a one-year period.
The increase in the index is attributed to rising interest rates and return-seeking asset volatility, according to a news release.
Also, according to NISA, the average funding ratio of the 100 largest plans rose to 85.5%, up from 84.7% in May.