"Or if you've replaced the tires recently with larger ones, that will throw off your odometer as well."
Or, if the OP has recently bought tires with a higher rolling resistance…
I am constantly amazed at how many people fail to look at the rolling resistance ratings on tires before buying them. A friend of mine phoned me just before he finalized the purchase of new tires for his Rav-4. In addition to the fact that the “recommended” tires had really high rolling resistance, they also had poor scores in terms of both traction and heat resistance.
Luckily, I was able to convince him to NOT buy these old-technology Bridgestone tires from STS Tire, and instead to buy the far-superior Michelin Defenders from a different retailer.