If an operational amplifier circuit consistently produces a lower output voltage than expected based on its specifications, what could be the underlying cause?

When an op‑amp circuit consistently outputs a voltage lower than the ideal calculation, the most common culprit is the amplifier’s limited ability to swing to the supply rails. Even if the datasheet says the output can reach the rails, real devices have headroom that keeps the signal a volt or two away from the rails, especially when the output must drive a load. Another frequent issue is that the op‑amp’s finite open‑loop gain and input offset voltage create a small error that grows with the closed‑loop gain, so the output is shifted downward. For example, if a 10× amplifier is powered from ±5 V, the output may only reach about ±4. 5 V, leaving a 0.