Take your next pill as soon as you remember, and use a back-up method for 7 days afterwards. If it was a non-hormonal pill during the 4th week, throw out the non-hormonal for that day and get back on schedule the next day.
If you have had sex since you got off schedule and that is within the last five days, you might want to take emergency contraception just in case.
References:
- Family Planning NSW. (2015). The Combined Oral Contraceptive Pill. Retrieved from https://www.fpnsw.org.au/sites/default/files/assets/combined_oral_contraceptive_pill.pdf