Model exposure, contact intensity, and protective measures quickly. Compare scenarios using consistent risk multipliers easily. Plan safer interactions by testing assumptions before meeting others.
This calculator estimates overall transmission probability by combining: (1) the chance the source is infectious, and (2) the chance transmission occurs given infectiousness.
| Step | Expression | Notes |
|---|---|---|
| 1) Source infectious probability | p_source = clamp(0, 0.99, prevalence × confidence × test_adjust) | Prevalence and confidence approximate the pool infectious fraction. |
| 2) Conditional transmission | p_cond = 1 − exp(− base_rate × hours × modifiers) | Uses an exponential dose-style model for incremental exposure. |
| 3) Single-contact probability | p_single = p_source × p_cond | Combines infectiousness probability and conditional transmission. |
| 4) Cumulative across contacts | p_cum = 1 − (1 − p_single) ^ contacts | Assumes similar contacts and approximate independence. |
Modifiers include route relevance, masks (respiratory), ventilation (ACH), distance, activity, protection status, hygiene, and barriers. Values are simplified to support comparisons.
These example scenarios illustrate how changing protections and ventilation can shift the estimate. Your results will differ based on inputs.
| Scenario | Key inputs | Typical pattern |
|---|---|---|
| Outdoor brief conversation | Outdoor, 10 min, 1–2 m, normal talking, no masks | Often lower conditional transmission than indoor settings. |
| Indoor office with decent ventilation | Indoor, 60 min, ACH 6, 1–2 m, normal talking | Ventilation can reduce risk versus poorly ventilated rooms. |
| Crowded indoor event | Indoor, 120 min, ACH 1, loud talking, close distance | Higher intensity and duration can raise risk substantially. |
| Sexual route with barrier + extra measure | Sexual route, barrier_plus, typical duration | Barrier and additional measures can lower modeled probability. |
Tip: For comparisons, keep prevalence fixed and only change one factor at a time.
Transmission risk starts with the probability that the source is infectious. The calculator uses community prevalence, recent symptoms, and test status to approximate this input. Higher prevalence raises the baseline chance before any contact details matter. Symptoms increase infectious likelihood, while a recent negative test reduces it. This step represents uncertainty about who is infectious, not how exposure occurs. When data limited, choose conservative values to avoid underestimation.
The next component models how efficiently a pathogen can spread along a chosen route. Base hazard values differ for airborne, droplet, contact, and blood routes, then scale with exposure type. Duration converts minutes to hours, and risk grows with time through an exponential dose response. Close, prolonged, and direct exposures increase the effective hazard, while brief or indirect interactions decrease it markedly. More contacts increase opportunities across the day.
Environmental conditions modify the effective hazard through multiplicative factors. Ventilation and filtration reduce airborne concentration, while crowding and indoor settings increase shared air and surface loading. Distance reduces droplet transfer, and humidity can influence persistence. The calculator combines these elements into a single modifier product, so small improvements across several fields can materially lower the final estimate. For indoor events, upgrading ventilation and reducing occupancy are often synergistic.
Individual protections further reduce the conditional probability of transmission. Mask use is applied as source control, receiver protection, or both, multiplying reductions rather than adding them. Vaccination and prior immunity reduce susceptibility and often shorten infectious periods, so they lower overall transmission probability. The model also accounts for hand hygiene and surface disinfection for contact routes where these controls are most relevant. Selecting both-mask scenarios highlights the benefit of layered controls.
Results are presented as a single-contact probability and a cumulative probability across repeated similar contacts. Cumulative risk uses an independent-contact approximation that compounds small probabilities over multiple encounters. Use the score to compare scenarios, test mitigation options, and prioritize controls with the largest effect. For high-stakes settings, combine this tool with institutional guidance and professional judgment. Export results to document assumptions and communicate risk consistently.
Cumulative probability estimates the chance of at least one transmission across repeated similar contacts. It compounds the single-contact probability over the number of encounters, assuming each contact is independent and has comparable conditions.
Ventilation and filtration dilute and remove airborne particles. In the calculator, better air exchange lowers the effective hazard, especially for indoor, longer-duration exposures where shared air accumulates.
Use a recent, local estimate when available, such as a dashboard summary, workplace screening data, or a public health report. If uncertain, test a low, medium, and high value to see how sensitive the result is.
No. It is a scenario-based estimator for comparing conditions and controls. For clinical decisions, outbreak response, or legal requirements, follow official guidance and consult qualified professionals.
Yes. Keep the same baseline scenario, then change one factor at a time, such as masks, distance, ventilation, or contact count. The relative change helps identify the most effective, practical control bundle.
Key assumptions include independence between contacts, simplified route selection, and approximate modifier values. Real-world factors like behavior, fit and consistency of protections, and heterogeneous mixing can shift outcomes. Treat results as directional, not absolute.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.