Recycled ICs have become a major threat to the ICs used in safety critical systems. In the current state-of-the-art techniques, recycled ICs are detected by measuring the frequency, current, path delay or power-up values to estimate the HCI, BTI and EM effects on the transistors with age. Some of the state-of-the-art techniques require additional on-chip sensors to detect and estimate the age of an IC while others use existing logic like SRAM and Flip-flops to detect the recycled ICs. In this paper, we provide a methodology to detect a recycled IC and also to estimate its age by using the existing IO pad structures. For the first time, age is estimated by measuring voltage drop across the protection diodes present in IO pad structure. With this methodology, no additional sensors have to be added and hence there is no area overhead. With this proposed methodology, ICs that are used for a minimum period of a day can be effectively detected by using the concept of extended Kalman filtering technique for the first time in this domain. By stressing the part for five days, our proposed methodology can estimate the age of the IC aged between 1 month to 5 years with 95% percent of accuracy. © 2021 IEEE