With English pronunciation the ways to say ed can cause a lot of confusion for ESL learners.  The regular verbs in the simple past tense all end in ed.  However there are three different ways to say ed, three different sounds that you make, and those sounds depends on the sound at the end of the infinitive of the main verb.

ways to say ed

The three ways that ed is sounded out are:

‘id’ as in ‘We dated for about three months.’
‘d’ as in ‘The presentation displayed some shots of Los Angeles’
‘t’ ‘We stopped to buy some drinks.’

These rules help to explain which sound of -ed you should use at the end of a verb:
If a word ends with a ‘d’ or a ‘t’ sound before ‘ed’, you pronounce it as ‘id’. Note: you are adding an extra syllable to the word.
If a word does not end with a ‘d’ or a ‘t’, you do not pronounce it as an extra syllable.  Your just add the sound ‘d’ to the end of the verb.
Remember that we base our -ed sounds on the last sound, not the last letter.  For example, the word ‘coincided’ is pronounced as ‘id’ at the end, although the last letter is ‘e’.  However, the last sound is ‘d’.
words with ‘id’ endings:
completed
stated
created
jotted
plotted
You use the  ‘t’ to sound out  ‘ed’  if the word before the ‘ed’ ends in the sounds ‘p’, ‘f’, ‘s’, ‘ch’, ‘sh’, ‘k’.  For example:
‘p’           stopped
‘f’           laughed (note the sound at the end of the verb is ‘f’ even if the spelling is ‘gh’
‘s’           messed
‘ch’         hatched
‘sh’         crashed
‘k’           forked
The last of the ways to say -ed is to pronounce it as a ‘d’, and we can pretty much go by the rule that any other verb not ending int he above sounds are pronounced as a  ‘d’:
flowed
minced
dimmed
filmed

Learn these three simple rules and ways to say ed at the end of  regular verbs.  The way you decide which of the three way to says ed is dependent not on the last letter of the verb, but on the last sound.