Thutmose seized the opportunity.
He set up camp at the end of the day, but during the night arrayed his forces close to the enemy; the next morning, they attacked.
It cannot be established if the surprised King of Kadesh had managed to fully prepare for battle.
Even if he did, it did not do him much good.
Though his forces were on high ground adjacent to the fortress, the Egyptian line was arranged in a concave formation, consisting of three wings, that threatened both Canaanite flanks.
Both the Egyptians and the Canaanites are estimated to have had around 1,000 chariots and 10,000 infantry.
The Pharaoh led the attack from the center.
The combination of position and numbers, superior maneuverability of their left wing along with an early, bold attack, broke the enemy's will; their line immediately collapsed.
Those near the city fled into it, closing the gates behind them.

The Egyptian soldiers fell to plundering the enemy camp.
During the plunder they captured 924 chariots and 200 suits of armor.
Unfortunately for the Egyptians, during this confusion, the scattered Canaanite forces, including the kings of Kadesh and Megiddo, were able to rejoin the defenders inside the city.
Those inside lowered tied-together clothing to the men and chariots and pulled them up over the walls.
Thus, the opportunity of a quick capture of the city following the battle was lost.

The city was besieged for seven months and the King of Kadesh escaped.
Thutmose built a moat and a wooden palisade, eventually forcing its occupants to surrender.
At Karnak it is recorded that the victorious army took home 340 prisoners, 2,041 mares, 191 foals, 6 stallions, 924 chariots, 200 suits of armor, 502 bows, 1,929 cattle, 22,500 sheep, and the royal armor, chariot and tent-poles of the King of Megiddo.
The city and citizens were spared.
A number of other cities in the Jezreel Valley were conquered and Egyptian authority in the area was restored.
Thutmose seized the opportunity. He set up camp at the end of the day, but during the night arrayed his forces close to the enemy; the next morning, they attacked. It cannot be established if the surprised King of Kadesh had managed to fully prepare for battle. Even if he did, it did not do him much good. Though his forces were on high ground adjacent to the fortress, the Egyptian line was arranged in a concave formation, consisting of three wings, that threatened both Canaanite flanks. Both the Egyptians and the Canaanites are estimated to have had around 1,000 chariots and 10,000 infantry. The Pharaoh led the attack from the center. The combination of position and numbers, superior maneuverability of their left wing along with an early, bold attack, broke the enemy's will; their line immediately collapsed. Those near the city fled into it, closing the gates behind them.
The Egyptian soldiers fell to plundering the enemy camp. During the plunder they captured 924 chariots and 200 suits of armor. Unfortunately for the Egyptians, during this confusion, the scattered Canaanite forces, including the kings of Kadesh and Megiddo, were able to rejoin the defenders inside the city. Those inside lowered tied-together clothing to the men and chariots and pulled them up over the walls. Thus, the opportunity of a quick capture of the city following the battle was lost.
The city was besieged for seven months and the King of Kadesh escaped. Thutmose built a moat and a wooden palisade, eventually forcing its occupants to surrender. At Karnak it is recorded that the victorious army took home 340 prisoners, 2,041 mares, 191 foals, 6 stallions, 924 chariots, 200 suits of armor, 502 bows, 1,929 cattle, 22,500 sheep, and the royal armor, chariot and tent-poles of the King of Megiddo. The city and citizens were spared. A number of other cities in the Jezreel Valley were conquered and Egyptian authority in the area was restored.
Battle of Megiddo (15th century BC)