The COLA is usually announced in October to give Social Security and other benefit programs time to adjust January payments. The Social Security Administration has given no indication that raises would be delayed because of the shutdown, but advocates for seniors said the uncertainty was unwelcome.
Social Security benefits have continued during the shutdown.
More than one-fifth of the country is waiting for the news.
Nearly 58 million retirees, disabled workers, spouses and children get Social Security benefits. The average monthly payment is $1,162. A 1.5 percent raise would increase the typical monthly payment by about $17.
The COLA also affects benefits for more than 3 million disabled veterans, about 2.5 million federal retirees and their survivors, and more than 8 million people who get Supplemental Security Income, the disability program for the poor.
Automatic COLAs were adopted so that benefits for people on fixed incomes would keep up with rising prices. Many seniors, however, complain that the COLA sometimes falls short, leaving them little wiggle room.
David Waugh of Bethesda, Md., said he can handle one small COLA but several in a row make it hard to plan for unexpected expenses.
"I'm not one of those folks that's going to fall into poverty, but it is going to make a difference in my standard of living as time goes by," said Waugh, 83, who retired from the United Nations. "I live in a small apartment and I have an old car, and it's going to break down. And no doubt when it does, I'll have to fix it or get a new one."
Since 1975, annual Social Security raises have averaged 4.1 percent. Only six times have they been less than 2 percent, including this year, when the increase was 1.7 percent. There was no COLA in 2010 or 2011 because inflation was too low.
By law, the cost-of-living adjustment is based on the Consumer Price Index for Urban Wage Earners and Clerical Workers, or CPI-W, a broad measure of consumer prices generated by the Bureau of Labor Statistics. It measures price changes for food, housing, clothing, transportation, energy, medical care, recreation and education.
The COLA is calculated by comparing consumer prices in July, August and September each year to prices in the same three months from the previous year. If prices go up over the course of the year, benefits go up, starting with payments delivered in January.
This year, average prices for July and August were 1.4 percent higher than they were a year ago, according to the CPI-W.
Once the September report, the final piece of the puzzle, is released, the COLA can be announced officially. If prices continued to slowly inch up in September, that would put the COLA at roughly 1.5 percent.
Several economists said there were no dramatic price swings in September to significantly increase or decrease the projected COLA. That means the projection shouldn't change by more than a few tenths of a percentage point, if at all.