Adequate intake of high-quality protein is important for maintaining muscle health and support healthy ageing [1, 2]. Protein quality is primarily determined by its composition in essential amino acids (EAA) relative to human requirements, as well as the digestibility [2]. Existing protein-quality measures generally assess individual foods or meals and may not capture amino acid complementarity across the total daily diet [2, 3]. This study aims to develop and apply a Daily Protein Quality Score (DPQS) that evaluates whether daily intake provides sufficient EAAs to meet personalised requirements. Dietary data will be drawn from 1650 Australian adults aged ≥65 years who participated in the 2011–13 Australian National Nutrition and Physical Activity Survey. Dietary data from up to two 24-hour recalls will be used to derive total protein intake (g/day and g/kg/day) as well as protein intake from either animal or plant-based food sources (g/day and percentage of total protein intake). Digestibility-adjusted EAA intakes for each meal will be calculated using the AlphaTool [3] and summed across meals for the whole day. Personalised EAA targets will be calculated using body weight and the 2007 joint World Health Organization, Food and Agriculture Organization, United Nations University Expert Consultations adult amino acid reference pattern [4]. For each day, digestibility-adjusted intake of each EAA will be compared with its corresponding target. The DPQS will be determined by the EAA with the lowest percentage adequacy, thereby identifying the most limiting EAA for that day. DPQS will be expressed as a daily protein quality score ranging from 0-100, with a score of 100 or above indicating the highest protein quality with no limiting EAA. Analyses will characterise the distribution of DPQS values and identify the EAAs that most commonly limit daily protein quality. DPQS will also be examined according to total protein intake (g/day), protein intake relative to body weight (g/kg/day), sex, age, and the proportion of protein derived from plant and animal sources (g/day and percentage of total protein intake). This will help identify dietary patterns and population groups with relatively higher or lower daily protein quality. Sensitivity analyses using alternative protein reference intakes will assess how DPQS values and their interpretation vary across different intake thresholds. Together, these analyses will help identify groups and dietary patterns at greatest risk of inadequate digestible EAA intake and determine whether overall daily protein quality adequately reflect current protein requirements and recommendations.