Use the same time points
Reference and test profiles should be compared at the same sampling times. Do not mix unmatched or interpolated rows unless the analysis plan justifies it.
Formulation Tools · Dissolution · Bioequivalence Support
Dissolution Profile Comparison Calculator
Calculate f1 difference factor and f2 similarity factor from matched reference and test dissolution profiles, with practical checks for common FDA and EMA caveats.
Quick Answer
The f2 similarity factor compares mean reference and test dissolution profiles at matched time points: f2 = 50 × log10(100 / sqrt[1 + (1/n)Σ(Rt − Tt)²]). Values ≥50 commonly indicate similar profiles when variability, unit count, and sampling design meet FDA/EMA expectations—but f2 alone does not guarantee regulatory acceptance. The f1 difference factor reports average percent difference relative to the reference profile. Use both with SUPAC, BCS biowaiver, and post-approval change evidence—not as a standalone BE decision.
Model-independent comparison
f1 and f2 equations
f1 = [SUM |Rt - Tt| / SUM Rt] x 100
f2 = 50 x log10(100 / sqrt[1 + (1/n) SUM (Rt - Tt)^2])
Rt and Tt are the mean reference and test percent dissolved values at the same sampling time. This tool compares mean profiles only; it does not evaluate unit-level variability.
Interactive Dissolution Calculator
Enter paired dissolution values by editing the table or pasting CSV-style rows: time, reference %, test %.
f1 Difference Factor - Lower indicates less difference.
f2 Similarity Factor - f2 >= 50 is a similarity signal with caveats.
Profile Assessment - Review method, variability, unit count, and product-specific guidance.
| Time | Reference % | Test % | Absolute difference | Squared difference |
|---|
Calculation Flags and Caveats
How to Use This Calculator
1
Enter matched time points — Add each dissolution sampling time once, using the same time points for the reference and test profiles.
2
Enter percent dissolved values — Enter mean percent dissolved for the reference and test products at each time point. Values should be between 0 and 120 percent.
3
Calculate profile factors — Run the calculator to compute f1 and f2 and review validation flags for plateau points, rapid dissolution, and profile design caveats.
4
Verify variability and unit count — Confirm each profile used 12 dosage units (typical regulatory example) and that CV limits are acceptable before treating f2 ≥ 50 as supportive evidence.
5
Interpret with caveats — Treat f2 values of 50 or greater as a similarity signal, not a standalone regulatory decision. Check current FDA, EMA, ICH, and product-specific guidance.
Worked Example
Immediate-release prototype vs reference batch
For profiles at 5, 10, 15, and 20 minutes with reference values of 42, 67, 84, and 91 and test values of 39, 64, 80, and 89:
f1 = 4.23 and f2 = 67.32. The f2 value is above 50, so the profiles are mathematically similar under the f2 rule of thumb, subject to unit-count, variability, media, sampling, and guidance caveats.
f2 Interpretation Bands
| f2 value | Interpretation | Regulatory use |
|---|---|---|
| ≥ 50 | Similar by conventional threshold | May support SUPAC, development, or biowaiver evidence if variability and design assumptions are met |
| < 50 | Not similar by conventional threshold | Investigate formulation/process differences; do not rely on profile similarity alone |
| Any value | Not a standalone BE verdict | Requires full study design review, product type rules, and agency-specific expectations |
Rules and Caveats for f2 Interpretation
Use 12 units per profile
Regulatory examples commonly describe mean dissolution profiles from 12 dosage units for each product. This calculator uses means and cannot verify unit count.
Check variability limits
Common f2 guidance expects coefficient of variation limits of not more than 20% at early time points and not more than 10% at other time points.
Limit plateau weighting
Only one sampling point after 85% dissolved is typically used, so the plateau does not dominate the f2 calculation.
Rapid dissolution may be different
For rapidly dissolving products, profile comparison may not be needed in some cases when both products dissolve sufficiently quickly under specified conditions.
Bootstrap high variability
When variability is high, bootstrap f2 confidence intervals or other justified methods may be more appropriate than a single point estimate.
Do not treat the calculator output as regulatory acceptance. f2 is one part of a broader quality, bioequivalence, post-approval change, or biowaiver justification.
Pharma / CMC Context for Formulation Scientists
Dissolution profile comparison is a workhorse tool in pharmaceutical development, tech transfer, and post-approval change assessment. Formulation teams use f1/f2 when comparing prototype batches, evaluating scale-up impact, or documenting similarity after equipment or site changes under SUPAC-IR frameworks. Analytical and QA groups should pair calculator output with validated dissolution methods, apparatus calibration, and statistical review of unit-level data.
Profile similarity connects to upstream blend and compression quality. Investigate content uniformity drift with our Blend Uniformity Calculator, compression-related dissolution risk with the Tablet Compression Troubleshooting Guide, and excipient changes that may alter release with the Excipient Compatibility Checker.
For regulatory submissions, document the full dissolution method, sampling rationale, individual unit results, and justification when f2 is or is not applied. Bioequivalence decisions remain protocol- and product-specific.
Evidence & Sources
- FDA: Dissolution Testing of Immediate Release Solid Oral Dosage Forms
- FDA: BCS-based biowaiver guidance for immediate-release solid oral dosage forms
- FDA: SUPAC-IR guidance for scale-up and post-approval changes
- EMA: Guideline on the Investigation of Bioequivalence
- ICH M9: Biopharmaceutics Classification System-Based Biowaivers
Competitive landscape: Generic f2 calculator spreadsheets and academic BE tools compute the similarity factor but often omit FDA variability limits, plateau-point warnings, and SUPAC/BCS context. NovaPharmaNews adds validation flags, worked examples, and cross-links to blend uniformity, compression troubleshooting, and excipient compatibility within a free pharma formulation workflow.
Frequently Asked Questions
The f2 similarity factor is a logarithmic, reciprocal square-root transformation of the mean squared difference between reference and test dissolution profiles. Values of 50 or greater are commonly interpreted as indicating similar profiles, but only when the comparison design and variability assumptions are appropriate.
The f1 difference factor expresses the average percentage difference between two dissolution profiles relative to the reference profile. Lower values indicate less difference between the test and reference profiles.
At least three shared dissolution time points are needed for the mathematical f2 calculation. In regulatory use, the selected time points should be the same for both profiles and should characterize the dissolution curve without over-weighting plateau values.
No. An f2 value of 50 or greater can support a similarity argument, but agencies also consider study design, sampling times, variability, units tested, product type, dissolution medium, and current guidance expectations.
For rapidly dissolving immediate-release products, some guidance frameworks allow profile comparison to be unnecessary when both products dissolve sufficiently quickly under specified conditions. Confirm the current product-specific FDA or EMA expectation before relying on that pathway.
High variability can make conventional f2 comparisons inappropriate. Alternative approaches such as bootstrap confidence intervals or model-independent multivariate methods may be considered when justified and aligned with regulatory expectations.
FDA dissolution guidance commonly references CV limits of not more than 20% at early time points and not more than 10% at other time points for the individual unit data underlying mean profiles. This calculator uses mean profiles only—you must verify unit-level variability separately.
Including multiple plateau points can overweight late-time similarity and mask meaningful differences during the rising portion of the curve. Regulatory practice typically limits comparison to one sampling point after 85% dissolved in at least one profile.
SUPAC-IR guidance uses dissolution profile similarity as supporting evidence when assessing certain scale-up and post-approval changes in formulation, manufacturing site, process, or equipment for immediate-release solid oral dosage forms. f2 is one element within a broader change level and documentation framework.
For eligible BCS Class I or III immediate-release products, similar dissolution profiles across relevant pH media may support a biowaiver argument alongside solubility, permeability, excipient, and product risk assessments per FDA and ICH M9 guidance. Profile similarity alone is insufficient.
f1 measures average absolute percent difference relative to the reference sum and is intuitive but sensitive to profile shape weighting. f2 is a log-transformed similarity metric with a conventional threshold of 50. Agencies often expect f2; f1 may appear as supplementary evidence in development reports.
Reference and test profiles should be compared at the same sampling times using mean values from the same dissolution conditions. Interpolation or unmatched rows require justification in the analysis plan and are not handled by this calculator.