Tell us the part number of your opamp and I will show you in its datasheet where it shows its max output low voltage.
The lousy old 741 opamp is still popular. On the datasheet for the MC1741 (single 741 opamp) and MC1458 (dual 741 opamp) it shows a max output low voltage that is 4V above the negative supply voltage and shows a graph of the typical output low voltage of 2V above the negative supply voltage.
Texas Instruments invented the TL081 so their datasheet has more information than other manufacturers who simply copy it.
They show the max output voltage with different supply voltages, different load resistors and different temperatures.
You didn't say your supply voltage but if it is 12V then the graph in the datasheet shows a typical output low voltage that is 1V above the negative supply if the load is 10k ohms or more. It could be as high as 3V if the supply is 30V.
Alright, thanks. I'm still a little confused. I think I need to learn how to read those charts and relate them to real world application a little better.
The graph on the right side shows that with a plus and minus 6V supply (12V total) and a 10k load, the output typically goes down to 1V above the -6V supply which is ground in your circuit. Some are slightly better and some are much worse.