I’m a new landlord in CA and missed the 21 day window to return the security deposit (I thought I had 30 days).

I paid it...Didn't  find a buyer and lost the deposit. 

Quote from @Marc Brandon: How much was the deposit?

The differences in bed/bath counts actually do not matter that much, but typically sqft does.If you are off by even $100/mo per unit rent-wise, this could turn an 8% CoC return into a 3% CoC return instantly - in which case you'd have been better off just putting your money in the S&P500 and not a rental property.

You get an estoppel from each tenant saying this is how much rent I’m paying, this is how big a security deposit I gave, here’s who pays for utilities, when my lease ends, etc etc. 

So I made a compromise with myself, instead of putting that $100 directly to my principle, I'm opening a brokerage account that will have $100 deposited into it automatically every month and invested in index funds using dollar cost averaging method.

Consider all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

The information is provided in 'how to get your security deposit back at the end of your lease' language.  

If you're going for non full documentation loans then there are other methods to qualify as well (rental income/ bank deposits/profit and loss/no income/etc) but these loans have higher rates and costs typically.

Are there deposits on file?