Opioid Conversion Calculator — Equianalgesic Dose
Rotate between opioid medications by entering the current drug and daily dose, selecting the target opioid, and applying a 25–50% cross-tolerance safety reduction — the calculator shows the estimated equianalgesic starting dose and CDC risk level.
Current opioid (convert from)
mg/day
Target opioid (convert to)
%
Equianalgesic dose after cross-tolerance reduction — confirm with prescriber
- 1
Source MME/day
20 mg/day × 1.5 = 30 - 2
Cross-tolerance reduction
30 × (1 − 25 ÷ 100) = 22.5 - 3
Estimated target dose
22.5 ÷ 1 = 22.5
How does this calculator work?
Convert opioids by translating the source dose to MME using CDC 2022 factors (oxycodone ×1.5, morphine ×1.0, fentanyl patch ×2.4 per mcg/h), reducing by 25–50% for incomplete cross-tolerance, then dividing by the target factor. Always confirm with a clinician before prescribing.
Formula
How this is calculated
Opioid rotation (switching from one opioid to another) is performed to improve pain control, reduce side effects, or manage tolerance. The standard method uses morphine milligram equivalents (MME): each opioid is expressed as a multiple of oral morphine using CDC 2022 clinical conversion factors (oxycodone ×1.5, hydromorphone ×4.0, fentanyl patch: mcg/h × 2.4, etc.). The source dose is first converted to MME, giving a common currency to compare potency.
Because patients are not fully cross-tolerant between opioids, the calculated equianalgesic dose is then reduced by 25–50% before converting to the target drug. A 25% reduction is typical for most rotations; 50% is used for high-dose patients or those who are elderly or medically frail. This adjusted MME is divided by the target opioid's conversion factor to give the estimated starting dose.
Methadone is handled with a dose-dependent step-wise factor (CDC 2022: 4 MME/mg for ≤ 20 mg/day, rising to 12 MME/mg above 60 mg/day) because its accumulation in tissues makes it disproportionately more potent at higher doses. All results here are clinical estimates for reference — actual prescribing must involve direct assessment by a qualified clinician.
Frequently asked questions
Tolerance developed on one opioid does not transfer completely to a different opioid (incomplete cross-tolerance). If you simply substitute the full calculated equianalgesic dose, the new drug is effectively stronger than expected, risking overdose. Reducing by 25–50% errs on the safe side and the dose is then titrated to effect.
Methadone is a highly lipophilic drug that accumulates in body fat and has an extremely long, variable half-life. Its effective potency relative to morphine increases with dose: at low doses the ratio is ~4:1, but above 60 mg/day it can reach 12:1. The CDC 2022 step-wise table captures this non-linearity.
Methadone conversion carries particular risk because its pharmacokinetics are highly variable between patients. The result here is an estimate to prompt discussion — rotation to methadone should only be initiated by a specialist experienced with methadone prescribing.
Also known as
TG we-Calculate Editorial Team. (2026). Opioid Conversion Calculator — Equianalgesic Dose [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/opioid-calculator
TG we-Calculate Editorial Team. "Opioid Conversion Calculator — Equianalgesic Dose." TG we-Calculate. 2026. https://we-calculate.com/calculator/opioid-calculator.
TG we-Calculate Editorial Team, "Opioid Conversion Calculator — Equianalgesic Dose," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/opioid-calculator
@misc{wecalculate_opioid_calculator, title = {Opioid Conversion Calculator — Equianalgesic Dose}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/opioid-calculator}}, year = {2026}, note = {TG we-Calculate} }
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