Yes, it's January 2013 income, but the ES payments can be spread through the four TY 2013 payments.

Phil
Rule Your Retirement Home Fool

As always, Phil advice is correct.

Just a comment, because I am acquaited with a couple of people who have a history of tax issues. If the beneficiaries have seen their income decrease, they might be tempted to defer estimated payments and spend the money. It isn't your problem, but depending on how well you know who is asking for advice encouraging them to make all of the estimated tax payment might be appropriate.