Earned value management compares planned work with actual work accomplished to measure project performance. It calculates schedule variance by comparing earned value to planned work, and cost variance by comparing earned value to actual costs. Positive variances indicate the project is ahead or under budget, while negative variances mean it is behind or over budget. Indices like SPI and CPI also measure performance, with values over 1 meaning ahead or under budget and values under 1 meaning behind or over.