Before Fuelly can calculate MPG for individual fuel-ups, it needs a full tank to work from. Fuelly calculates an individual fuel-up MPG by using the difference from full. Your first fuel-up was marked as a partial, so Fuelly can't calculate an MPG for that fuel-up or the next one. The fuel-up you just added was full, so on your next full fuel-up you'll get an MPG calculation. Here's more info: Why do I have to fill the tank all the way up every time I buy fuel?