On my rental property, if I deducted the cost of improvements on my taxes during the year it occurred, can I also add it to my cost basis when I sell the rental?

[LudwigVan_fan]

The short answer would be no.

If you deducted the cost, and also add it to your basis, that would amount to a double deduction.

depending on the type and amount of improvements made, they possibly should be capitalized and depreciated or amortized.  The question is very general, therefore a specific answer can't be given in terms of whether to deduct or capitalize.  But you certainly can't deduct and then also add to basis.

For some guidance on repair (deduction) vs. improvements, here is a link to Pub 527

https://www.irs.gov/publications/p527

[beauguard]

When I sell my rential propertity , can I reduce my capital gain for the loss in past YRS?

[beauguard]

What is the answer?

[JamesG1]

It depends.  If you deducted the losses in prior years, you don't get to deduct them again.

However, you may be able to deduct passive activity losses from previous years tax returns when you sell the property that generated them. 

See Deducting Passive Activity Losses in this TurboTax Help.

“If your rental property has generated losses in past years, you might have suspended passive activity losses (PALs). You can generally deduct these passive losses only against passive income, which can be from other activities such as rentals or other passive business activities.

Fortunately, you can also deduct suspended PALs when you sell the property that generated them. If you sell a rental property with suspended PALs, you may be able to deduct them on top of deducting any Section 1231 loss from the sale. Like Section 1231 losses, deductible PALs can offset other income and also create or increase an NOL that you can carry backward or forward.”  [Edited 2/23/20 11:08 AM] @beauguard