As you begin entering your peak week, your current level of carbohydrates will be different from the next bodybuilder. Even though there may not be an “exact formula” for the start of a peak week, for each person we can take a certain consistent approach.
During the weekend before the weekend of your contest, taper back your carb intake slightly (this can be by as much as 100 to as little as 25 grams depending on carb sensitivity) to allow your body to recover and prep your muscles for an influx of carbs on Monday, your highest carb day of the week. On Monday, you should consume 25 to 100 grams more than a regular dieting day of carbohydrates to force glycogen to be stored in your muscle tissue. This is predicated on your ability to consume carbohydrates.
By the middle of your peak week, around Wednesday and Thursday, your body will have reached a peak hardness look. For an ectomorph both Thursday and Friday may be used to increase carbs and increase muscle fullness. What’s worked well for me is to have Thursday be a day in which I consume more carbs, allowing me to taper back on Friday and regain a bit more tightness.
On the day of the show, you’ll use specifically timed meal combinations of protein, carbs, fat, water, and when needed, small additions of sodium to keep your muscles full, hard, and tight. Monitor your physique, carb sensitivity, and make the necessary tweaks. After all, by now you are lean enough and understand the level of carbs your body can or can’t handle.