Mixed — yoga as physical exercise is not inherently sinful. Yoga as explicit Hindu spiritual practice is a different question. Most Western gym yoga falls in between. Assess the specific practice, not yoga as a category.
The question "is yoga a sin?" requires distinguishing between at least three different things that all carry the word "yoga": (1) yoga as a Hindu spiritual practice with specific religious intent, (2) yoga as a physical fitness practice that uses the same postures without Hindu spiritual content, and (3) yoga as a New Age spiritual practice that blends Hindu and Western spirituality. These are genuinely different things requiring different assessments.
Classical yoga is inseparable from Hindu spirituality — the postures (asanas), breathing (pranayama), and meditation practices are designed to facilitate union with Brahman (the Hindu concept of the divine). The word "yoga" itself means "union" in Sanskrit. When yoga includes Sanskrit chants, meditation on mantras, instruction in chakras or kundalini energy, or meditation aimed at altered states of consciousness, it has crossed from exercise into spiritual practice that conflicts with Christian monotheism and Deuteronomy 18's prohibitions on occult spiritual practices. Christian theologian Albert Mohler has addressed this concern directly.
Many Christians practice yoga purely as physical exercise — stretching and strength training using poses derived from yoga tradition without any spiritual content. Whether this is acceptable is a genuine disputable matter (Romans 14). Some Christians argue the postures cannot be separated from their spiritual origin; others argue physical movement is physical movement regardless of cultural origin (1 Corinthians 10:25-27 — "eat whatever is sold in the meat market without raising questions of conscience").
Practical guidance: if your yoga class includes Sanskrit chants, spiritual instruction, meditation aimed at emptying the mind, or discussion of chakras and energy — it has moved into spiritual territory requiring discernment. If it is genuinely physical exercise with no spiritual content — it is a disputable matter of Christian conscience. See our meditation guide for the distinction between Christian and Eastern meditation, and our Is It a Sin? hub.
Questions about sin fall into two categories: things explicitly called sin in Scripture, and disputable matters (Romans 14-15) where Christians with different convictions should respect each other's consciences. Even when something isn't explicitly sinful: Does this practice reflect Christ's lordship over all of life (Colossians 3:17)? Is it beneficial — not just permissible? (1 Corinthians 10:23). Score: 55/100 Mixed.
See our Is It a Sin? hub. GotQuestions and the Gospel Coalition provide thorough evangelical analysis.