i know some investors probablyevery month calculate how much tax they will owe on april 15.

anyone have good rule of thumb?   like 25% of gross rent? 

I use a software (purposefully not mentioning name due to potential bp rule breaking as I've plenty of those) that calculates my estimate tax payments for the following year and I can print coupons out as reminders with the amount. It can be quarterly or monthly. If you go over its a definite refund but even if you fall a bit short you should still be ok and may just have to add the difference. **Find ways to have expenses as a self-employed taxpayer....

Kudos,

Mary