What would be my 100-day plan to get a 6 pack?First you need to work out your current body fat levels. If you're a man you need to be around 8% BF for a six pack, for females this will be 15-17%
Once you know your body fat you should be able to work out how much fat you need to lose to get to 8%, notice I said fat not weight.
To lose fat without losing much muscle you need to diet slowly and steadily as such....
Find out your basal metabolic rate - eat at a caloric deficit of 3000-4000 per week, in order to lose around 1lb per week.
Slowly reduce your calories over the course of the 100 days (every 7-10lb weight loss, recalculate your BMR). If weight loss stalls don't panic, it usually means you're eating too little not too much. Just take a week or so off dieting (but don't go hog wild) to give your body a break and then get back on it.
Training wise focus on getting stronger and supplement some abs exercises into the mix after every session. Train 3-4 times per week. Big compound lifts like deadlift and bench press are your staples here. Avoid cardio!!!!