Background: Energy intake (EI) is historically underreported with traditional methods (e.g., self-report, dietary recall). Recent technological advancements allow for objective physical activity (PA) devices to be utilized in back-calculation formulas to estimate EI. However, energy expenditure (EE) can be measured as the [sum of active kcals + resting metabolic rate (RMR)] or total kcals. While most researchers use the sum of active kcals + RMR to back-calculate EI, limited research has explored whether EI estimates using this method vary in comparison to other measurements of EE, such as total kcals. Given the lack of published data on device algorithms for these PA variables, a possible discrepancy in how EI is back-calculated could result in under- or over-estimations of EI. This variability could have implications for weight-control interventions such as the Healthy Mom Zone (HMZ) Study, one of the few adaptive interventions to utilize device-based PA and principles of control systems engineering to estimate EI and predict gestational weight gain in pregnant persons with overweight/obesity. This study purpose was to compare mean EI estimates when back-calculated with the sum of active kcals + RMR compared to total kcals among a sample of pregnant individuals. Methods: Pregnant participants (N=9) from the HMZ 2.0 pilot study wore a Fitbit Charge 6 device 24 hours/day for 5 consecutive weeks. Mean daily active kcals + RMR and total kcals and respective EI estimates were calculated for all participants. Mean differences between EI estimates with active kcals + RMR vs. total kcals were analyzed using paired t-tests. Results: Back-calculated EI with active kcal + RMR was significantly higher than back-calculated EI with total kcal (Mdiff= 588.84 kcal, range: 21.84-1161.79 kcal), p=0.003. Higher EI estimates using active kcal +RMR were observed on 100% of measurement days with significant differences on 60% of days. Conclusions: Back-calculating EI with active kcals + RMR results in higher estimates of EI compared to when EI is back-calculated with total kcals. Careful consideration should be given to which measurement of EE is used in the EI back-calculation formula. Future research is needed to replicate these findings and understand potential implications for weight-based interventions.