"Need" to for what? If you're in a calorie deficit (either through diet or calories burned- diet is easier) you'll lose weight. End of story (there are other reasons to exercise, but if you're only worried about losing weight, just cut your calories- safely). You can calculate your calorie allowance by using a BMR or daily calorie calculator, such as the one here: (this is from Steve's signature)
I wouldn't worry about your own perception. You see yourself every day so it's hard to see the differences as they'll be so incidental over an hour-by-hour, day by day basis. Look to measurements (chest, waist, hips, other areas you're interested in), the scales, how your clothes fit, and what people (who you trust and who are going to be supportive/ give an honest opinion) say about your appearance, particularly those who you haven't seen for awhile.