A key metric in tuberculosis epidemiology is the annual risk of infection (ARI), which is usually derived from tuberculin skin test (TST) and interferon-gamma release assay (IGRA) prevalence surveys in children. Deriving the ARI assumes that immunoreactivity is persistent over time; however, reversion of immunoreactivity has long been documented. Here we use a deterministic, compartmental model of Mycobacterium tuberculosis (Mtb) infection to explore the impact of reversion on ARI estimation using age-specific reversion probabilities for TST and IGRA. Using empirical data of TST reversion (22.2%/year for 0-19yo), the true ARI is 2-5 times higher than estimated from immunoreactivity studies in 8-12 year-olds. Applying empirical reversion probabilities for IGRA (9.9%/year for 12-18yo) showed a 1.5-2-fold underestimation. ARIs are increasingly underestimated in older populations, due to the cumulative impact of reversion on population reactivity over time. Declines in annual risk did not largely affect the results. Ignoring reversion leads to a stark underestimation of the true ARI in populations and our interpretation of Mtb transmission intensity. Future surveys should adjust for reversion probabilities and its cumulative effect with increasing age to provide a more accurate reflection of the burden and dynamics of Mtb infection.