Methods and circuits for monitoring circuit degradation include measuring degradation in a set of on-chip test oscillators that vary according to a quantity that influences a first type of degradation. A second type of contribution to the measured degradation is determined by extrapolating from the measured degradation for the plurality of test oscillators. The second type of contribution is subtracted from the measured degradation at a predetermined value of the quantity to determine the first type of degradation for devices represented by the predetermined value.