計算曆法（arithmetic calendar）係用嚴格嘅數學公式計算嘅曆法，例如而家嘅猶太曆，亦稱為以規則為準嘅曆法，好處係容易計算特定時間是邊一日，不過同自然變化對應嘅精準性就比較差，即使曆法本身非常精準，亦會因為地球自轉及公轉嘅變化，累積偏差，因此一個計算曆法使用嘅期限有限，可能只有幾千年，之後就要用新嘅曆法系統代替。
The arithmetic calendar is a calendar calculated by strict mathematical formulas, such as the current Jewish calendar, also known as the rule-based calendar, the advantage is that it is easy to calculate which day a specific time is, but the accuracy corresponding to natural changes is relatively poor, even if the calendar itself is very accurate, it will also accumulate deviations due to the changes in the rotation and revolution of the earth, so a calculation calendar is used for a limited period of time, may only be a few thousand years, and then it will be replaced by a new calendar system.