No taxes owed on a home sale if you lived in it as your primary residence for at least two years.
$250,000 limit for individual, or $500k for a couple.

I know I owe tax on $145,000, but I don't know how to compute the tax itself. I found something online that, I think, says I have to pay 15% of that.

Thanks.

Not sure of income levels.
Either check it out online or call a tax adviser, who will of course want to charge you.

For example, if you hit the lottery for a million, your capital gains tax could be 20% instead of 15%.

Pretty sure I’m in the 15 percent range.

it might be a good year to hire a CPA. They may or may not be busy right now, as the extension deadline to file is October 15.

First you only pay tax on the Gain,
The original cost, plus closing costs are your 'cost basis'.
any major improvements or serious repairs, like new windows, replacing a roof. Smaller jobs like painting or light remodeling don't count.
then from the selling price you deduct any sales commissions, taxes and fees from the sale.
then your gross taxable profit is reduced by $250K if your single. finally there is a slightly graduated scheme in schedule D where the capital gain is taxed.
Estimated is due quarterly, but you only have to prepay 100% of last years liability each quarter, Or 90% of current estimate, which ever is lower.

https://smartasset.com/investing/capital-gains-tax-calculator

https://finance.zacks.com/calculate-capital-gain-selling-house-3027.html

I will check these out. It also seems helpful to figure out a schedule D.

And have you lived in it as your primary residence for 2 of the past 5 years.

I'm not sure what I paid. I think it was about $295,000. I know when the sale went through, I still owed $227,000 on the mortgage.

On edit: The sale paid off my mortgage, and I got about $165,000 in my bank account after the mortgage was paid.

You owe zero in taxes to the federal government on taxes. You would only have 100,000 in capitol gains at the maximum.

I just have to figure out how to find out for sure how much I bought it for. I imagine there are records somewhere. I didn't bring that paperwork when I moved.

You can go to Zillow.com. Put in your address and they may still have the sales history. It may not be an exact number but close enough for city work.