Thanks for using the forum.
It is possible for a woman's cycle to be a little off from time to time. Sometimes stress, life changes, weight changes, diet changes and other causes can cause hormone fluctuations that lead to irregularities.
If your period does not come in the next few days, the best and most accurate time to test for pregnancy is one week after the first day of your missed period. At this time the pregnancy hormone is usually high enough to be detected in the urine.
Hope this helps.
Cathy