penalty for underpaying your taxes - Rough estimate

Hello

If I owe the government about $1,500 for taxes, can anyone do the rough math on how much the penalty will be? I only earned 13k in contracting for the whole year of 2025.

They will just email me a letter stating the amount of penalty and I pay it?

I do plan adjusting my w-4 through my w-2 employer so this can be avoided.