What is the formula for absolute bioavailability?

Absolute bioavailability (F) = (AUC_oral / Dose_oral) ÷ (AUC_iv / Dose_iv) × 100%. It compares the systemic exposure of a non-IV route against the fully bioavailable IV route.

What is relative bioavailability?

Relative bioavailability compares two non-IV formulations using the same formula: (AUC_test / Dose_test) ÷ (AUC_ref / Dose_ref) × 100%. A value near 100% indicates similar exposure between the two formulations.

What AUC units should I use?

Both AUC values must be in the same units (e.g., both in ng·h/mL or both in µg·h/L). The dose units must also match each other (e.g., both in mg). The calculator works with any consistent unit system.

Can bioavailability exceed 100%?

Absolute bioavailability should not exceed 100% under normal conditions. However, relative bioavailability can exceed 100% if the test formulation produces greater exposure than the reference — for example, due to a supersaturating formulation or a food effect.

What does an AUC ratio represent?

The AUC normalized by dose (AUC/dose) represents systemic exposure per unit dose. Dividing the test ratio by the reference ratio cancels out dosing differences and isolates the fractional absorption difference between routes.

What is a typical oral bioavailability value?

Oral bioavailability varies widely: some drugs like alendronate are below 1%, while others like propranolol are around 25%, and drugs like metoprolol can reach 50%. A value above 80% is generally considered high oral bioavailability.

Bioavailability Calculator

Enter AUC and dose values for two routes to calculate absolute or relative drug bioavailability as a percentage.

Bioavailability Inputs

Enter AUC and dose for both routes. Units must be consistent.

Calculation Type

Absolute (vs. IV) Relative (vs. Reference)

Test Route (e.g., Oral)

AUC_test

Dose_test

Reference Route (IV)

AUC_ref

Dose_ref

Result

Enter values and click Calculate to see results.

Absolute Bioavailability

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0% 50% 100%+

Calculation Breakdown

Parameter	Test Route	Reference Route
AUC	—	—
Dose	—	—
AUC / Dose	—	—

Formula: F (%) = (AUC_test / Dose_test) ÷ (AUC_ref / Dose_ref) × 100

Bioavailability Reference Ranges

Classification	Range	Example Drugs
High	≥ 80%	Metronidazole, Venlafaxine
Moderate	40 – 79%	Metoprolol, Fluoxetine
Low	10 – 39%	Morphine, Propranolol
Very Low	< 10%	Alendronate, Vancomycin (oral)

Summary

Bioavailability measures the fraction of an administered drug dose that reaches systemic circulation in an unchanged form. Absolute bioavailability compares a non-intravenous route (e.g., oral) against an intravenous reference, while relative bioavailability compares two non-IV formulations. Both calculations normalize the Area Under the Curve (AUC) by dose to account for different amounts administered.

How it works

Select the calculation type: absolute bioavailability (requires IV reference) or relative bioavailability (compares two non-IV routes).
Enter the AUC value for the test route (e.g., oral AUC in ng·h/mL).
Enter the dose administered via the test route.
Enter the AUC value for the reference route (e.g., IV AUC).
Enter the dose administered via the reference route.
The calculator applies the standard pharmacokinetic formula and displays bioavailability as a percentage.

Use cases

Pharmacy students learning pharmacokinetics concepts.
Researchers comparing oral vs. IV drug formulations in preclinical studies.
Pharmacologists evaluating the bioavailability of a new drug candidate.
Clinicians checking whether a generic formulation is bioequivalent to a brand-name drug.
Veterinary pharmacologists calculating bioavailability across species.
Nutritionists estimating mineral or supplement absorption from different sources.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu