I wake up in the morning and enter into prayer, offering the fast to God for … (the intentions). A one day fast lasts through the night until the next meal I take the following day. I have low blood sugar, so I can do a strict fast, but I have to take in something. I have coffee (because I need the sugar or I’ll wind up in the hosital) and bread. That’s allowed for medical reasons… (the coffee)… When it ends depends on what you are fasting for… Here’s my thoughts, but they are personal opinion, not Church teaching. Deeper understanding 1 to 9 days. Depends on the topic and your receptivity to the answers. Repel the attacks of the evil one 3 days before confronting (at least). As an offering of thanksgiving or anything like that 1 or 2 days. Before a major decision, depending on the decision… 1-9 days, but averaging 2-3. Lent 40 days, but not a strict fast. A fast from what you’ve given up and an addition of virtues God wants you to focus on. It’s also not a bad idea to just talk it over with God and see what He thinks. I used to be so proud of myself for completing a fast when I first began to come into to the Catholic Church. Wow! was I way off base. The Lord showed me the starving who eat 1 meal a week and all of a sudden, I began to focus on the heart and the surrender, much more than what I considered ignorantly to be the intensity of the sacrifice. Don’t worry. If you’re His… He perfects even your most humble or imperfect efforts. And if you forget or cave… don’t worry. Pick yourself up, dust yourself off, acknowledge it to Jesus and begin again if that’s what He wants for you.