How Much To Spend Fixing Up House in between Tenants

[Ray King]

Hello Everyone,

How do you figure out a budget for fixing up a house in-between tenants?

Long term tenants are moving out end of the month, July 2020. 

Single-family home (3 bedroom/1 bath) with a detach in-law (1 bedroom/1bath).

Due to COVID not sure how long it will take to rent, and should this time be used to do some improvements that could affect the overall property value?  

Is there a "formal" to use figuring out the dollar amount to spend for the return to gain?

Thank you.