The use of cost vs. costed as the past tense of cost over time in the Google Books corpus

If this continues, eventually “cost” will become a regular past tense verb.

Which do you say?

• It cost $12.

• It costed $12.

Note that there’s a difference between the use of costed meaning ‘to estimate the cost of something’, e.g. “we found out the project was unfeasible after we costed it out”, vs. the meaning ‘to have a price of’. The phrase it costed, which I used in the Google Ngrams search, is typically only used in the latter sense.

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