###### Abstract
In an effort to guide what needs to be measured regarding CBE, [PERSON] et al. [17] identified six CE principles: (1) reduce reliance on fossil resources, (2) use resources efficiently, (3) valorize waste and residues, (4) regenerate, (5) recirculate, and (6) extend the high-quality use of biomass. They also set nine measurement requirements: (1) share of renewable resources, (2) resource use efficiency, (3) degree of regeneration, (4) degree of recirculation, (5) utility, (6) risk of accumulation of hazardous substances, (7) effect on environmental protection, (8) effect on economic viability, and (9) effect on social equity. Within the EU's Horizon Europe R&D program, the BIORADAR project is developing a digital tool to monitor the sustainability and circularity of bio-based products. A part of its innovation is the building of a circularity monitoring framework that puts the spotlight on often-overlooked circularity aspects within the bio-based fertilizer, textile, and packaging industries. It considers several of the CE principles and measurement requirements identified by [PERSON] et al. The BIORADAR project identified that there have not been many advancements in measuring circularity at the product level in bio-based sectors. In fact, a systematic literature review [18] identified 11 indicators applied to bio-based products, without sector differentiation. Another systematic literature review conducted within BIORADAR identified 29 indicators that were specifically applied to bio-based fertilizers, textile and packaging materials; however, 26 of them were indicators designed for general purposes and not specifically for bio-based applications. The three indicators that indeed were designed for the bio-based industry focused on waste management systems that produce fertilizers, mostly focusing on nutrient recovery and overlooking other relevant CE items. These results confirm previous research highlighting shortcomings in the circularity indicator appropriateness for biological cycles [19; 20]. Therefore, the main research gap to be addressed is the limited capacity of existing circular economy monitoring tools to capture the specificities of the biological cycle--particularly when assessing the circularity of bio-based products. This gap highlights one of the most pressing challenges in operationalizing the circular economy concept: moving from a macro-level perspective, where several indicators are already available, to product-level assessments, where bio-based products are still evaluated using tools originally developed for conventional materials from the technical cycle. As a result, critical aspects of bio-based circularity remain overlooked. To address the mentioned gap, this manuscript aims to put forward the BIORADAR product circularity monitoring framework as a managerial tool envisioned to foster the industrial transition toward a more sustainable and circular economy, specifically within the bio-based fertilizer sector. Given the lack of bio-based-specific measurement tools to guide the circular transition within bio-based industries, the results and conclusions of the study present a validated way to measure CBE-relevant aspects of the bio-fertilizer industry, thereby bridging the identified knowledge gap and contributing to the ongoing quest and debate. Through this study, the BIORADAR product circularity monitoring framework was demonstrated to be applicable to bio-based fertilizers, and its results proved to supply relevant insights on virgin non-renewable material consumption, waste generation, biodegradability, nutrient recovery efficiency, and nutrient release speed.