How to calculate the intermediate power for computer glasses from the near vision prescription?

Subtract 1.00: The intermediate strength is the reading prescription minus 1 diopter typically. However, your eye doctor can adjust this strength based on the actual distance your computer sits from you.

Usually one-half: Not too difficult. Take one-half of the add power (the near power) and add it to the basic power (e.g. -4.00 for basic and +1.25 for add equals -2.75 for the computer power). Slightly more complex if you have significant astigmatism, the final power in the above case for computer bifocals would be upper power = -2.75 and near power +1.25).