Thinker,
You really need to pencil this out. Your question is on estimated taxes, but you have been paying in taxes with your salary, and if your pension will start up in July, you can continue to pay in taxes through your pension.
If you decide to do withholding using your pension, then the question becomes how much additional income will you have over and above the tax due on both salary and pension. You can use a tax prep program to tell you how much that is, and then determine if you need to make an estimated tax payment or payments.
Last year was my first full year in retirement -- but -- I got a small bonus payment due from the year prior on which tax was withheld, I get a small pension on which tax is withheld, AND I did a partial IRA to Roth conversion. So, I used the annualized income method that Audrey describes because my taxes were significantly lower than the year before.
If you have reasonably good Excel skills, and some time, you can set up the calculations to figure out the estimated taxes due in each quarter based on your income and expenses in each quarter.
Once set up, you'll need to track and record both income and expenses to have the spreadsheet determine the tax payment. Last year, I found I only needed to make two estimated payments, based on the timing of income and expenses in each quarter.
I wouldn't expect you would use this method this year, but you know what income you have coming in and its timing.
-- Rita
P.S. This year I'll continue a partial Roth conversion, and having estimated the income, I've set up four quarterly payments through EFTPS. Less fuss, less muss!