The change in stance is likely to comfort analysts, who pressured the company earlier this year for more disclosure on its exposure to disasters. At that time, Allstate executives said it had been hard to come up with a way to report such losses.
The company said on Thursday that it will now provide monthly and quarter-to-date updates any time a monthly loss exceeds $150 million.
Over the last 10 years, Allstate said, monthly losses have crossed that threshold about 30 percent of the time.
While it is common for insurers and especially reinsurers to disclose their catastrophe exposure after major events, it is unusual for an insurer of any kind to commit to monthly loss updates.
The April loss is substantial -- roughly equal to Allstate's total catastrophe losses for the full second quarters of 2010 and 2009 combined. With the worst part of tornado season yet to begin, the losses could rise.
In a statement, Allstate said it experienced 13 loss events in April in the United States and Canada, with the worst being a tornado outbreak in the U.S. South in the last week of the month.
More than 100,000 claims have been filed to date, the company said.
Allstate shares fell 1.3 percent to $32.62 in early trading, their lowest point in about two weeks.
(Reporting by Ben Berkowitz, editing by Gerald E. McCormick and John Wallace)