I sold a rental property in 2019. Can i differ the capital gain if I buy another rental property. How long do i have to differ the Capital gain?

[DoninGA]

You can differ the capital gains through a 1031 Exchange, but only if you follow the rules -

https://www.investopedia.com/financial-edge/0110/10-things-to-know-about-1031-exchanges.aspx

There are two key timing rules you must observe in a delayed exchange.

1. The first relates to the designation of a replacement property. Once the sale of your property occurs, the intermediary will receive the cash. You can't receive the cash, or it will spoil the 1031 treatment. Also, within 45 days of the sale of your property, you must designate replacement property in writing to the intermediary, specifying the property you want to acquire. The IRS says you can designate three properties so long as you eventually close on one of them. You can even designate more than three if they fall within certain valuation tests.
2. The second timing rule in a delayed exchange relates to closing. You must close on the new property within 180 days of the sale of the old. Note that the two time periods run concurrently. That means you start counting when the sale of your property closes. If you designate replacement property exactly 45 days later, you'll have just 135 days left to close on the replacement property.