Whether you get a subsidy will depend on your family size, your adjusted gross income (AGI), and a little bit on where you live.
For your family size, this is you, plus any spouse, plus any dependents that you will have in 2021.
Your AGI for the ACA will probably be whatever you will have on your tax return on line 8b for 2021. It's essentially your taxable income minus some adjustments such as HSA and traditional IRA contributions.
Once you have those two numbers, you can look at this link to see where you family falls in terms of something called the federal poverty level, or FPL:
https://thefinancebuff.com/federal-poverty-levels-for-obamacare.html
ACA subsidies exist for AGIs up to 400% of the FPL, so if you were a family of two and lived in the mainland of the US, you would see the number $17,240. That's the FPL, so ACA subsidies exist up to 4 times that number, or $68,960.
The subsidy is on a sliding scale up to that 400% number. There are breakpoints in the formula at 150%, 200%, 250%, and 300% of the FPL.
You can probably find out what your subsidy will be by going to your state's ACA marketplace (it's a website - just google your state's name plus ACA marketplace and the link should be obvious, or you can start at healthcare.gov) and putting in your information.