Abstract Aim: To assess the reliability of fluid balance charts in neonates. Methods: An observational study in 170 nonbreastfed neonates, requiring continuous monitoring on a high‐care unit, but not critically
ill. The fluid balance was compared to daily body weight changes using Bland–Altman analysis. Differences more than 20% of daily fluid intake were considered clinically relevant. Results: The mean gestational age was 36 + 2 weeks (SD 18.7 days) and
mean birth weight 2782 g (SD 749 g). The mean difference between 394 fluid balances over 24 h (in mL) and daily weight changes (in g) was −12.1 (limits of agreement −128.1 to 103.8). In 40% of comparisons, the difference with daily weight change was more than 20%
of daily fluid intake. Conclusion: Fluid balance charts both over‐ and underestimate body weight changes in an unpredictable pattern and are therefore unreliable as a single measure of fluid status in neonates.