Usually after “short” vowels in words with more than one syllable.
add odd Rudd |
adder addict adding address adduce bedding bidden bidder bidding bladder budding cheddar cladding cuddling diddling dodder faddist fiddler fiddling fodder gladden gladdest goddess haddock hidden huddling kidding ladder madden madder maddest meddling midden middling muddling nodding oddball odder oddest oddment oddness paddling paddock plodded plodder plodding prodded prodding pudding puddling redden reddest reddish riddance ridding sadden sadder saddest shedding shredded shredder shudder skidding sledding sodden studded studding sudden thudded thudding toddler trodden udder wadding waddled waddling wedding |