JOHNSTON, R.I.–Factory Mutual Insurance Co., which does business as FM Global, will credit its policyholders with an estimated $380 million when they renew their policies next year, the Johnston, R.I.-based insurer announced Wednesday.

In a statement announcing the “membership credit,” FM Global said that the credit “is a result of the company’s excellent operating performance due, in large part, to policyholders’ effective loss prevention efforts.”

FM Global will have credited a total of nearly $1.3 billion to its policyholders with this being the fourth membership credit since 2001.

Eligible policyholders will receive the 2008 credit in the form of a premium reduction at the time of their policy renewal or annual anniversary next year.

The size of the credit depends on policyholder tenure, with those having held policies for fewer than five years receiving a 5% credit, those who have held policies for five to 19 years receiving a 10% credit, and those who have held policies for 20 or more years receiving a 15% credit.