Like others have covered, your fuel burn will be the greatest during your initial climb and early phases of cruise because you’re at your heaviest weight. It requires a great deal of thrust to keep your aircraft aloft at these weights and at a speed your demanding. Because of this, you have your power set higher to maintain a given speed.
But do not worry. You might be showing that you’ll be a few hours short on fuel to your destination shortly after establishing cruise. As your aircraft burns fuel, you are reducing the weight of the aircraft. Because you are at a lesser weight, this requires less thrust to keep the aircraft aloft at your given speed.
Take this example: I departed on a flight that I know is 15hrs in length. But in the first 1hr of the flight, I might be showing 12 hrs of fuel at my current fuel burn/flow. This is because I’m still heavy. As I near my destination, I notice that I’ve got 4 hrs of fuel left. That’s at least another 4 hrs of flying past my destination. Reasoning: Aircraft is lighter and as a result fuel burn lower because less thrust is needed to keep the aircraft flying at said altitude and speed.
There are a great deal of tutorials that cover “Fuel” related matters in the #tutorials section of the forum. These have been of help to others and I hope these can help you as well.
Fuel planning is discussed in this topic as well: 👇🏼