ESL Blogs

(from my e-book, "Speak and Write Like a Native: 110 Things You Need to Know About English")
7) Pronunciation of “-ed” endings:   The past simple tense and past participle of all regular verbs end in -ed.  ESL students very often pronounce this ending as a separate syllable, but in many cases this –ed ending is not pronounced as a separate syllable.
 
The rule here is:
Verbs ending in “t” or “d” ( “want”,  “treat”,  “sound”,  “end”,  “add”, etc.)  gain a syllable when put into the past tense:
“want-ed”,  “treat-ed”,  “sound-ed”,  “end-ed”,  “add-ed”
Verbs ending in any other consonant ( “play”,  “allow”,  “beg”,  “laugh”,
“watch”,  “hope”,  etc.) do not gain a syllable when put into the past tense:
“played”,  “allowed”,  “begged”,  “laughed”,  “watched”,  “hoped”

And note that this second group of verbs has two possible end-sounds: “-d” and “-t”.   
e.g. “played”,  “allowed”, and  “begged” have a “-d” end-sound:  
“playd”,  “allowd”,  “beggd”
but “laughed”,  “watched”, and “hoped” have a “-t” end-sound:  
“laft”,  “watcht”,  “hopt”