This sounds a little "too cute" for me. The only safe harbor that could apply to most people for a $10k amount is that you paid 100% of the previous year's liability. So, you could only really do this every-other year, and really only if you had $0 liability in the alternating years. So you'd have to be able to alternate between $0 liability one year, and $10k+ liability the next year. For the other safe harbor, you'd have to have a $100k tax liability for 90% to be $10k. If your income is that high, you probably aren't on this message board.