How to use (3 steps)
- Select an example or enter [S] and v in the table (Excel paste OK).
- Confirm units and adjust advanced settings (weights, initial values) if needed.
- Km, Vmax, and plots (fit/residuals) are shown.
Linearization (e.g., Lineweaver–Burk) can distort error handling. Use nonlinear fitting as the main estimate and linearization as a reference.
Input ([S] and v)
—
—
| [S]（—） | v（—） | Actions |
|---|
Blank rows are ignored. Enter values ≥ 0.
Paste (TSV/CSV)
Paste two columns ([S], v). A header row (S, v) is allowed.
Advanced settings
Initial values are guides for stable fitting. If it does not converge, try changing them.
Results (Km, Vmax)
Results will appear here.
——————SSE=—, RMSE=—, R²=—Outputs
Plots (fit & residuals)
Hover (or tap) a point to see details.
Per-point table
| [S] | v | v_fit | residual | residual² |
|---|
How it’s calculated
- Model:
v = (Vmax × [S]) / (Km + [S]) - Estimate Km and Vmax by minimizing the sum of squared residuals (nonlinear least squares).
- R² and RMSE are shown as guides to fit quality.
How to use this calculator effectively
This calculator is designed to make scenario checks fast. Use a repeatable workflow: baseline first, one variable change at a time, then compare output direction and magnitude.
How it works
Run your first scenario with defaults. Then, change exactly one assumption and observe which result changes most. That is the fastest way to identify sensitivity and explain what drives the outcome.
When to use
Use this page when you need practical planning support, side-by-side alternatives, or a clean baseline for further discussion.
Common mistakes to avoid
- Changing multiple assumptions simultaneously.
- Confusing percent and decimal inputs.
- Mixing unit systems across scenarios.
- Relying only on rounded display output for final conclusions.
Worked example
Prepare a base case and one alternative case, then compare outputs and validate the direction, scale, and interpretation with the same assumptions across both cases.
See also
FAQ
How many points do I need to fit?
Because two parameters (Km and Vmax) are estimated, at least 3 points are recommended. More points usually improve stability.
The fit does not converge. What can I do?
Try adding high-concentration points, widening the [S] range, checking possible outliers, or changing initial values.
Is a high R² always correct?
It is a guide, but R² alone is not definitive. In nonlinear regression, R² can be negative if the fit is worse than a mean model. Check residual patterns and [S] range too.
Can I fit with different units?
Yes. Units are labels only; changing units does not convert entered values. Choose labels that match your numbers.
What is included in the share URL?
Settings (units, weights, bounds, initial values) and optionally input data.
Are my inputs sent anywhere?
All calculations run in your browser. Your data is not sent.
How to use Michaelis–Menten fitter (Km, Vmax) effectively
What this calculator does
This page is for estimating outcomes by changing inputs in one controlled workflow. The model keeps your focus on variables, not output shape. Start with stable assumptions, then test sensitivity by changing one key input at a time to observe directional impact.
Input meaning and unit policy
Each input has an expected unit and a typical range. For reliable interpretation, check whether you are using the same unit system, period, and base assumptions across all runs. Unit mismatch is the most common source of unexpected drift in numeric results.
Use-case sequence
A practical sequence is: first run with defaults, then create a baseline log, then run one alternative scenario, and finally compare only the changed output metric. This sequence reduces cognitive load and prevents false pattern recognition in early experiments.
Common mistakes to avoid
Avoid changing too many variables at once, mixing incompatible data sources, and interpreting a one-time output without checking robustness. A single contradictory input can flip conclusions, so keep each experiment minimal and document assumptions as part of your note.
Interpretation guidance
Review both magnitude and direction. Direction tells you whether a strategy moves outcomes in the desired direction, while magnitude helps you judge practicality. If both agree, you can proceed; if not, rebuild the baseline and verify constraints before deciding.
Operational checkpoint 1
Record the exact values and intent before you finalize any comparison. Confirm the unit system, date context, and business constraints. Compare outputs side by side and check whether differences are explained by one changed variable or by hidden assumptions. This checkpoint often reveals the single factor that changed everything.
Operational checkpoint 2
Record the exact values and intent before you finalize any comparison. Confirm the unit system, date context, and business constraints. Compare outputs side by side and check whether differences are explained by one changed variable or by hidden assumptions. This checkpoint often reveals the single factor that changed everything.
Operational checkpoint 3
Record the exact values and intent before you finalize any comparison. Confirm the unit system, date context, and business constraints. Compare outputs side by side and check whether differences are explained by one changed variable or by hidden assumptions. This checkpoint often reveals the single factor that changed everything.
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