If you're lucky! How thick the lining of the uterus gets in the couple of weeks before you get your period is what determines how light, heavy, long, or short it will be. Since most of us ovulate each month, the hormone levels that grow that lining are similar each month so our periods are pretty consistent. Some months though, if you don't ovulate or if your hormone levels are lower for other reasons (like big weight loss, heavy exercise, big stresses in life), you may find you have a shorter or lighter period than normal.
Periods can be light and last 7 days or be heavy and last only 3. It really just depends on the person. For most women, periods usually last between 3-5 days - heavy the first 2-3 days and very light on the last. But it’s not uncommon to have longer periods along the lines of 5 or 6 days with a heavy flow. It feels like it would never end! It’s not a bad idea to keep a pad on for 2 extra days just in case your body is playing some kind of tricks on you.
As long as your period is lasting about 3 or more days, chances are you're just fine. But if you normally have gushers and this one is a trickle, and you're sexually active (or anything close to it), be sure to do a pregnancy test! Sometimes, in early pregnancy, you can have a really light period, so if this period is really different than usual for you, don't ignore it.
Some girls will have short and light periods every month and that's just who they are. Lucky them! Once again, it's all about what your body is going to do. Just keep an eye on it, and don't take it for granted that every time it will be this light. Just in case, carry pads with you because you just never know!
Source disclaimer: Article is adapted from original article source U by Kotex - USA