Amount used for rental purchase divided by amount of loan = portion allocated ("traced") to rental property.

Dump the 10T regs into a bowl with the 8T regs and sprinkle a CCM on top.

https://www.law.cornell.edu/cfr/text/26/1.163-10T

https://www.law.cornell.edu/cfr/text/26/1.163-8T

https://www.irs.gov/pub/irs-wd/1201017.pdf

Tracing rules are so much fun in late March.

If you allocate the percent of the interest to the rental property can you also deduct the amount used to purchase the rental property from the total loan for purposes of the $1,000,000 home loan limitation?

I don't know offhand. But you might be at the $750K limit now after the cash out refi.

Mixed-use mortgages and tracing rules are not for the faint of heart.  There aren't many simple answers, it all depends on the results of your tracing.

When I'm feeling too well and need an excuse to get out of something, I go reread the 163 regs.  Guaranteed migraine.