The 500 Rule (aka 450 Rule) from Using Insulin and the Pocket Pancreas is a great way to estimate how many grams of carbohydrate will be covered by one unit of Humalog or Novolog insulin. This is your insulin to carb ratio or your carb factor. Once you know this, you can count the grams of carb in the food you want to eat and divide by your carb factor to find how many units of bolus insulin are needed to cover the carbs. This alloiws flexibility in your food choices because any number of carbs can be covered with a matching dose of insulin.
When your blood sugar goes unexpectedly high, a correction bolus can be used to bring it down. To use the right correction bolus, you first determine your correction factor. The 1500 Rule for Regular was originally developed by Paul Davidson, M.D. in Atlanta, Georgia. Because the blood sugar tends to drop faster and farther on Humalog and Novolog insulins, we modified the 1500 Rule to an 1800 Rule for these insulins. (Some use a 2000 rule for these insulins.) The 1800 Rule shows how far your blood sugar is likely to drop per unit of Humalog and Novolog insulin. The 1500 Rule shows how far it will drop per unit of Regular.
A great advantage of frequent injections and insulin pumps is the convenience of giving additional insulin any time a need arises. A bolus can be given for dinner then again more for an unplanned dessert and more for the high blood sugar that follows.
Although there are no perfect answers, almost all Type 1s, and most people with Type 2, on insulin find their control is best when their long-acting insulin (Lente, NPH, Ultralente, or the basal rate on a pump) makes up 55% to 60% of their total daily insulin dose. This level lets you skip meals, and still keep your blood sugars relatively level.
With your health care provider's help, select a target range for before meals, 2 hours after meals, and at bedtime. Constantly aim for reasonable target ranges for your day to day blood sugars. Your target range covers the numbers you would like your blood sugars to stay within at least 75% of the time. This starting range can be tightened and improved gradually until you are ready for a more ideal range.