Brain tumors are unwonted and unbounded multiplication of cells. Brain tumor reports for 85% to 90% of all primary Central Nervous System tumors. There is a need for bio-medical imaging computational tools that performs processing and extracting clinically relevant facts and figures from patient's brain MRI images. Magnetic resonance imaging (MRI) provides detailed information about brain tumor anatomy, cellular structure and vascular supply, making it an important tool for the effective diagnosis, treatment and monitoring of the disease. This paper presents a computer aided detection tool for brain tumor using brain MRI images and assists the neurologists to plan the further treatment. This tool automatically perform pre-processing of MRI images using Gabor filter, edge detection and feature extraction using Canny edge detector algorithm and finally classify the tumor using KNN classifier. In addition, this computational tool aids in classifying the stage of tumor and approximate survival time of patients. The experimental results of proposed technique shows better results with 93% accuracy compared to state of art methods.