We introduce a calculus for handling integer arithmetic in first-order logic. The method is tailored to \Java\ program verification and meant to be used both as a supporting procedure and simplifier during interactive verification and as an automated tool for discharging (ground) proof obligations. There are four main components: a complete procedure for linear equations, a complete procedure for linear inequalities, an incomplete procedure for nonlinear (polynomial) equations, and an incomplete procedure for nonlinear inequalities. The calculus is complete for the generation of counterexamples for invalid ground formula in integer arithmetic. All parts described here have been implemented as part of the KeY verification system.