Hi synaps, regarding estimating the tax paid, it can be difficult when income is inconsistent. If your K-1's are routinely showing losses, then that can be "helpful" in that they won't add to your taxable income. Most people tend to estimate based on previous years, but of course when your investments are changing year to year that isn't always easy. If you are able to slightly overpay, that may be best for a few years until you can get a baseline. You will of course get any overpayment back in a refund or you can apply to the next year's estimates.
100% of payments do need to be paid by April 15, anything still owed after that would be charged late payment penalties and interest. The 90% rule only applies to whether you paid estimates on time, not whether you still have a payment due after April 15.
Here is a link to the IRS calculations on late filing penalties - https://www.irs.gov/payments/failure-to-pay-penalty
Let me know if you have any further questions!
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
