You've probably heard that you'll find the cheapest airfare on a Tuesday. But according to a new study from travel startup Hopper, that's a myth. So when can you find the best fares? Hopper monitored ticket prices from the month of January to find that the answer to that for both domestic and international travel is Thursday. Saturday, on the other hand, turns up the most expensive fares for domestic flights and Sunday is the priciest for international trips. The price difference, however, wasn't too terrible—you're looking at about $10 in savings between the best and worst days for domestic and about $25 for international. But hey, savings is savings.