Introduction: Acute kidney injury (AKI) with fluid overload is associated with poor outcomes. While percentage fluid overload (PFO) using intake/output charts (PFO<sub>i/o</sub>) has been validated as a marker of overload, accurate PFO<sub>i/o</sub> measurements may not be possible in a general ward. We propose an alternative weight-based PFO calculation: PFO<sub>w</sub> = [(maximum weight − baseline weight) ÷ baseline weight] × 100%. Methods: This is a prospective, observational pilot study on general ward inpatients with AKI who were referred for nephrology consult. PFO<sub>w</sub> was compared with PFO<sub>i/o</sub>, and both were evaluated for associations with dialysis requirement, AKI stage 2 or 3, and 90-day mortality. Results: Fifty-eight patients with a median age of 67.5 years (interquartile range 18.0) were recruited. Of which, 33 (56.9%) were males and 41 (70.7%) had preexisting CKD 3 or higher. We found no correlation between PFO<sub>i/o</sub> and PFO<sub>w</sub> ( R<sup>2</sup> = 0.015, p = 0.531). A higher PFO<sub>w</sub> was observed in AKI stage 2 or 3 ( p = 0.005) and in patients requiring dialysis ( p = 0.001). On multivariate analysis, each percentage increase in PFO<sub>w</sub> was associated with increased odds of AKI stage 2 or 3 (odds ratio 1.37 [95% CI 1.05–1.78], p = 0.020) and dialysis need (odds ratio 1.69 [95% CI 1.20–2.39], p = 0.003). Twenty-nine patients had complete quantitative data to calculate PFO<sub>i/o</sub>. Multivariate analysis of these 29 patients showed that PFO<sub>w</sub> correlated with AKI stage 2 or 3 and dialysis requirement, while PFO<sub>i/o</sub> had no correlation with these events. The area under the curve receiver operating characteristics of PFO<sub>w</sub> was 0.706 for AKI stage 2 or 3 and 0.819 for AKI requiring dialysis. The optimal PFO<sub>w</sub> cutoff was determined at ≥1%. Three deaths occurred within 90 days, and all had PFO<sub>w</sub> ≥ 1%, although the log-rank test did not achieve statistical significance ( p = 0.050). Conclusion: The proposed PFO<sub>w</sub> is a potential prognostic indicator for general ward patients with AKI. PFO<sub>w</sub> ≥ 1% is associated with poor renal outcomes.