Fairly quick taper.
From a stable dose of methadone, reduce by 5mg a day until you stop. From 20mg down use alpha-2-adrenergics (preferably lofexidine, if available, otherwise clonidine). On the 20mg methadone day take 2 0.2mg pills lofexidine (Britlofex) each pill being 0.2mg) or 2 0.1mg pills clonidine [clonidine is available in other doses, but I shall assume henceforth that a pill of lofexidine is 0.2mg and a pill of clonidine is 0.1mg] at bed time. On the 15mg day take 2 pills (either clonidine or lofexidine) at lunch time, and 2 at bed time (4 total). On the 10mg day take 2 pills each at lunch, tea time and bed time (6 pills total), and on the 5mg day take 2 pills each at breakfast, lunch, tea time, and bed time (8 pills total). Continue taking 8 pills a day for 8 more days, then 6 (miss out lunch pills), then 4 (miss out lunch and tea pills), then 2 (just take at night).

Very rapid taper
Good for other opiates where exact doses might be harder to calculate, or stabilization and gradual reduction is not plausible.

This is essentially the 20mg methadone down part of the last taper, with the 20mg dose replaced by your usual dose, 15mg by three-quarters of your usual dose, 10mg by a half of your usual dose, and 5mg by a quarter of your usual dose. The alpha-2-adrenergic agonists are given in the same 2 pills,4 pills, 6 pills, 8 pills for 8 days, 6 pills, 4 pills, 2 pills schedule.

[My cat has done variants of these last two, except his "very rapid taper" was 200mg, 100mg, 0 methadone, and only up to 6 clonidine pills a day. He got through, but says 200mg methadone a day or more may better be quit using the fairly quick taper]

Cold Turkey

As above, but take 3 lofexidine/clonidine pills on the last day of using opiates, 6 on the first day off, then 8 pills for 8 days, 6 pills, 4 pills, 2 pills.