Not all senior citizens will get their Social Security payment on the third day of the month anymore.

Instead, new retirees who first become eligible for Social Security this Thursday, May 1, or later will get their benefits on either the second, third or fourth Wednesday of each month, depending on their birthday.For senior citizens who were receiving benefits before May 1, and people who get Supplemental Security Income disability benefits - commonly known as SSI - the third-of-the-month payment date won't change.

Acting Social Security Commissioner John J. Callahan said he is phasing in the new payment schedule to prepare for the huge increase in the Social Security Administration's workload expected when baby boomers retire.

"As our beneficiary workload climbs from nearly 43.7 million today to 76 million by the year 2025, it is critical for us to change our payment pattern to maintain responsible, high-quality service," Callahan said in his announcement of the change Tuesday.

About half of Social Security beneficiaries get checks through the mail and half have the monthly payment - on average $745 - electronically deposited into their bank accounts. Besides getting the payments out, the Social Security Administration must field questions and complaints each month.

New retirees affected by the change - about 2.6 million this year - can still predict when their cash is due.

Those with birth dates between the first and 10th will get their benefits on the second Wednesday of each month. Those born between the 11th and 20th will always be paid on the third Wednesday, and those with birthdays the 21st through the 31st will get their money on the fourth Wednesday of each month.