2000 740i gas problem

Hello folks I just bought a 2000 740i it has around 107k on the mileage and I am wondering why it's burning so much gas. I park it overnight ad when I start the car the next morning it loses around 10-20 miles off my gas mileage. Could it be in need of a tuneup could the gas meter need recalibrating? Please respond if you've ever experienced this or have any advice.
Thank you.

Start with a full (and competent) service and tune. Then recheck your figures.

If you are just reading the milage left on your display it can vary easily by 20 miles after the car sits but once you drive it it will change again the computer judges your milage by the way you step on the gas so if your foot is to the floor less milage left in the tank etc.

Ditto...if you're looking at your OBC's RANGE figure...take another look when the engine reaches normal operating temps and see if the "range" has now increased to approximately where it was when you shut the engine down last.

The OBC is taking current calculations...and a "cold" engine is consuming more fuel than when it reaches normal operating temps. So yes, when you start the car in the morning, the OBC RANGE may show a drop in distance....but it should increase as the engine warms up.

Report back if this is true (the range increased as the engine warmed up) so that we know that it was only new ownership jitters...and not another issue.

OBC Range Calculation info from owners manual

Yesterday was the only day I experienced the meter going back up after a 45 min drive to the city but the gas still dropped ridiculously I maintained a constant speed to and from the city I gained mileage on the way to the city but on the way back I lost a lot more miles. It just freaks me out not knowing how my gas is gonna be. I think I am gonna start with a full tune up and see where it takes me.