Verb Forms and Verb Tenses: Verb Forms and Verb Tenses (#8): Spelling Regular Past Forms

Add -d to the base form.

This happens when the base form ends in a vowel
and one or more consonants plus e:

ached, baked, blamed, breathed, cared, cached,
chased. diced, dozed, dyed, edged, fiddled, filed, 
glared, grated, hated, hoped, joked, lived,
mired, noted, paced, pasted, raced, raised,
sliced, spared, surprised, tasted, typed, whined.

This also happens when the base form ends in ue,
oe, or ie:

glued, rued, sued, hoed, toed, died, lied, tied

Change -y to -i and add -ed.

This happens when a verb ends in a consonant
and y:

apply / applied; bully / bullied; bury / buried;
carry / carried; copy / copied; cry / cried;
dry / dried; ferry / ferried; fry / fried;
hurry / hurried; marry / married;
parry / parried; pry / pried; query / queried;
rely / relied; tarry / tarried; tidy / tidied;
try / tried; vary / varied; worry / worried

This does not happen when a verb ends in a vowel
and y:

annoy / annoyed; bray / brayed; destroy / destroyed;
employ / employed; enjoy / enjoyed;
fray / frayed; gray / grayed; obey / obeyed;
play / played; pray / prayed; prey / preyed;
stay / stayed; stray / strayed; sway / swayed;
toy / toyed

Compare fray / frayed with fry / fried;
pray / prayed , prey / preyed and parry / parried
with pry / pried.

Double the final consonant and add -ed
if there is a single stressed vowel before
the final consonant.

ban / banned; can / canned; hem / hemmed;
mop / mopped; pin / pinned; sip / sipped;
trap / trapped; wad / wadded; whip / whipped;
compél / compélled; confér / conférred;
prefér / preférred; refér / reférred

Note:

Compare cane / caned and can / canned; 
mope / moped and mop / mopped;
pine / pined and pin / pinned;
wade / waded and wad / wadded.

Also compare óffer / óffered and confér / conférred;
trável / tráveled and compél / compélled.