2011年8月22日 · "Subtotal" is similar to "subcategory", where it means a "smaller part of a larger group"; in the former, the subtotal is a smaller group within the larger total, and the latter, subcategory is a smaller group within a larger category. –

Whichever way is standard for a given word. As a general rule, the hyphen is more likely to be used in situations where you're expected to read "sub-" as a separate unit, and it gets lost when the entire compound word gets common enough to be perceived as an entity in and of itself.

"Subtract" is the word. Though the obsolete word "substract" did exist, any occurrence you see these days is most likely just a common mistake, formed by analogy either with "abstract" or with other languages whose corresponding words do have two ‘s’s.

2023年5月10日 · "Subtotal" vs "total" 0. Why is the bill from my health care provider sometimes called a "factura"? 1. ...