* What: Wal-Mart de Mexico (Walmex) Q1 earnings poll

* When: Scheduled to report April 8 after market close

* Net profit seen up 12 pct to 3.285 billion pesos.

By Cyntia Barrera Diaz

MEXICO CITY, April 7 (Reuters) - Wal-Mart de Mexico, the top Mexican retailer, is expected to post a 12 percent rise in first-quarter earnings, helped by a calendar effect and an aggressive low-price campaign backing a government effort to fight inflation.

Analysts polled by Reuters forecast, on average, that Walmex earned 3.285 billion pesos ($309 million) in the January-March period, up from 2.943 billion pesos in the previous year quarter.

Starting 2008, all Mexican companies will post nominal results, meaning they will not adjust for inflation, in observance of new accounting rules.

"March posted very positive same-store sales results helped by two significant calendar impacts: the Holy week (being in March versus last year's April) as well as an additional Sunday," Credit Suisse said in a report.

February had an extra day because of Leap Year.