In the care of chronic kidney disease, the key is not the exact value of the glomerular filtration rate (GFR) at one time, but the rate of its decline. The last two decades have been devoted to refining the equations for estimated GFR (eGFR), which has improved disease classification and standardized communication between centers. However, determining the stage of the disease is only one part of care. Treatment decisions, risk stratification and preparation for dialysis depend on reliable monitoring of eGFR over time. The accuracy of the slope of the GFR decline may be more clinically important than the accuracy of a single measurement. In a prospective multicenter study (doi:10.1136/bmj-2025-085005), Scandrett and colleagues followed a large group of patients with moderate CKD (stage 3) in Great Britain.