Plantar fasciitis is usually diagnosed by clinical findings alone; if characteristic signs and symptoms are present the diagnosis is likely to be accurate.

• Ask about the nature of the heel pain, and the general health and physical activity of the person.
• Characteristic symptoms of plantar fasciitis include:
• An initial insidious onset of pain.
• Intense pain during the first steps after waking or after a period of inactivity.
• Lessening pain with moderate foot activity, but worsening later during the day or after long periods of standing or walking.
• Plantar fasciitis typically affects people 40–60 years of age who are overweight or obese, or who are on their feet for extended periods. Conversely, it may affect younger people who engage in sporting activities (e.g. running).
• Examine the foot at rest (when sitting), and when standing and walking.
• Tenderness on palpation of the plantar heel area (particularly, but not always, localized around the medial calcaneal tuberosity) is a defining sign of plantar fasciitis.
• Limited ankle dorsiflexion range (with the knee in extension) and a positive 'Windlass test' (reproduction of pain by extension of the first metatarsophalangeal joint) is suggestive of plantar fasciitis.
• An antalgic gait (abnormal walking to avoid pain) or limping may be observed.
• If clinical signs of plantar fasciitis are absent or inconsistent, consider an alternative diagnosis.
• Ask about recent or past trauma and recent changes in footwear, to rule out conditions such as fractures and sub-calcaneal bursitis.
• Examine the foot for physical abnormalities, including congenital abnormalities such as pes planus (flat foot) or pes cavus (high arch), tight Achilles tendon or signs of tendonitis, or skin changes which may indicate systemic disorders or infection.
• Investigation is only required to exclude alternative diagnoses.
• Consider testing for erythrocyte sedimentation rate, C-reactive protein, and Human Locus Antigen B27 for spondyloarthropathies, and referral to radiography for fractures.
• Bilateral plantar fasciitis is estimated to occur in up to 30% of people with the condition, but nevertheless should increase the degree of suspicion that there may be a systemic cause.