The rules for regular verbs in the past are the following.
 

	We normally add  -ed to the verbs	eg  work worked worked
	If the verb ends in  "e" we only add -d	eg  love loved loved
	If the verb ends in consonant +  y we remove the  "y" and add  -ied	eg  study studied studied
	With verbs of 1 syllable which end in  consonant + vowel + consonant we double the last letter.	eg  stop stopped stopped
	Note: For full information about verbs with two syllables please consult a book of grammar.