Is It a Mortal Sin? Check It Against the Catechism
You would not be checking this unless one particular act is weighing on your conscience, and that weight is a good sign: it means your conscience is awake.
A sin is mortal only when three conditions are all present at once: grave matter, full knowledge and deliberate consent (CCC 1857). Pick the act on your mind and answer the questions below. The checker sets your answers against the Catechism's own lines for that act and tells you what to do next, with every paragraph linked on vatican.va.
What the Catechism says
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What makes a sin mortal?
A sin is mortal when it involves grave matter, is committed with full knowledge that it is seriously wrong, and is chosen with deliberate consent. All three must be present together (CCC 1857). If any one is missing, the sin is venial (CCC 1862). Our guide to mortal vs venial sin gives examples of each.
Can this checker tell me whether I am in a state of grace?
No. The Church teaches that we can judge whether an act is gravely wrong, and must leave the judgment of persons to the justice and mercy of God (CCC 1861). Use the result to prepare for Confession, and let a priest help you weigh what a web page cannot.
Should I receive Communion if I think I committed a mortal sin?
Anyone aware of having committed a mortal sin should go to Confession before receiving Communion, unless there is a grave reason to receive and no way to confess first (CCC 1457). Until you can get there, pray an act of contrition out of love for God, with the firm intention to confess as soon as you can (CCC 1452).
What if I am afraid everything I do is a mortal sin?
That fear may be scrupulosity, a well-known affliction the Church treats gently. Choose one regular confessor, tell him about the fear and follow his guidance. Our guide to scrupulosity explains where to find help.
Where do the answers come from?
Every line about where the Church draws the line comes from the Catechism of the Catholic Church, and each result links the exact paragraphs on vatican.va. The acts and paragraphs were last checked in November 2026.