Investment market gains probably helped the typical large defined benefit pension plan do a little better in March.

The “funded ratio” at a typical plan was 3.5 percentage points higher at the end of the month than at the beginning, according to consultants at Towers Perrin Inc., Stamford, Conn.

A typical large pension plan may have ended March with only 64% of the assets needed to cover pension obligations.

Although the funded ratio was up a little at the end of March, it was still down from about 90% in mid-2008, Towers Perrin actuaries estimate.

Towers Perrin actuaries gauge pension plan health by estimating the performance of a hypothetical benchmark pension plan that invests 60% of its holdings in stocks and 40% in bonds and other fixed-income instruments.

The benchmark portfolio would have enjoyed a 5.5% return on investments in March, along with a 0.6% drop in pension benefit obligations liability, Towers Perrin actuaries report.