Is it safe to daisy-chain two 12-gauge extension cords?

Yes, but only for light to moderate loads. The bigger issue isn’t overload—it’s voltage drop. Two 12-gauge cords daisy-chained to 100 feet still handle 20 amps at the plug without overheating, but voltage drop can cause motors to run hot, lights to dim, and battery chargers to slow down. For heavy draws like a miter saw or welder, use a single 10-gauge 100-foot cord instead.