IRVINE, CA—Residential Realtors often say that homebuyers who close in the fall and winter months to get the best deal. The chalk it up to lighter competition from other buyers in these colder months when families are entrenched in the back-to-school schedule.

RealtyTrac recently took a big-data approach to checking the validity such conventional wisdom, and found the data to be in agreement, but with a few glaring exceptions.

The online data firm analyzed more than 32 million sales of single family homes and condos since 2000, and found that the month where buyers have gotten the best deal on average is October. Of the 2.7 million sales closed in October over the last 15 years, the average sales price was 2.6% below the average estimated full market value at the time of sale. Following October as best months to buy were February, July, December and January — all fall or winter months except for July, which was a surprise given that conventional wisdom would suggest that is a good time to sell but not necessarily to buy to buy at a bargain price.