IRS corrected my filing to a higher refund

A month after e-filing using Turbotax Home & Business, I received a direct deposit from the IRS for more than double what Turbotax's federal refund was supposed to be.  I have received no correction info from the IRS. While I'm not complaining about the higher refund, I'm concerned that Turbotax's calculations were not correct. Any suggestions for finding out where the difference in calculations may be?  Thanks.