Changing your major as a freshman or sophomore typically has few, if any consequences for your graduation date. However, for a junior or senior, it can have a serious impact. While underclassmen are still completing general education courses, most juniors and seniors have already begun taking classes for their major. If you spent a semester taking courses you find you don't need after changing your major, you could set your graduation date back significantly. If your school offers the class you need only once every two semesters, you could end up postponing graduation by a full year.
If changing your major results in spending more time at school, you are likely to incur more school-related expenses, such as tuition and textbooks. Students who use financial aid to pay for school may end up even deeper in debt when they have to borrow money to attend school longer than anticipated. If you change your major from something non-technical -- for example, in the social sciences -- to technical, such as computer science, you may incur technology fees or be required to purchase expensive equipment to complete your coursework.
The stressors often associated with changing your major are many. If you attend a large university, you may need to get to know an entirely new part of campus; finding your way around and getting to class on time can shake up your whole schedule. In addition, you may have the social stress of getting to know new classmates or professors. You may be required to fill out paperwork to complete the change. You may experience feelings of uncertainty or anxiety when starting your new major classes or fears that you will be "behind" your classmates academically.
If you wait until after your sophomore year to change your major, you may end up with wasted credit hours that won't transfer to your new major. For example, if you take a class on the New Testament, thinking you want to major in religion, it is not likely to transfer for credit when you change your major to physics. If you need to change your major, look for options in the same department, such as Humanities or Communications, as your current major to decrease the chance of wasting credit hours.