The last syllable of the regular past ED tense verb

Here is the rule:

Regular past tense verb endings are pronounced in 

three different ways depending on the final sound in 

the present form.

• The [id] sound: If the final sound in the regular verb is T or D:
  The past is pronounced as an extra syllable [ID].
  -ed: adds a whole syllable to a word.
  

  Example:

  wanted = want + [id]
  
  
• The [t] sound: If the final sound in the regular verb is a voiceless
  sound, the past is pronounced as [T], but not as
  an extra syllable.

  Example:

  watched = watch + [t]
  
  Otherwise,
• The [d] sound: If the final sound in the regular verb is a voiced sound,
  d - b - r - l - m - n - v or all vowel sounds,
  the past is pronounced as [D], but not as an extra syllable.
  

  Example:

  needed = need + [d]

• 80% of verbs with soft t sound or soft d sound.
  
• 20% where we put the stress (syllable): [id],