Life · Time
What time should I wake up to be on time?
On-time arrival probability simulator
Showers, breakfast, waiting and travel never take exactly the same time. Use your estimates of that variation to find an alarm time for your chosen on-time probability.
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How is this calculator different?
It is more than subtracting two fixed totals
Preparation and travel have day-to-day variation. This tool samples each step's usual time, longer-day time, range and rare delays to find wake-up times for different on-time probabilities.
Background calculation uses 65,536 deterministic samples. If the Worker is unavailable or fails, the on-device fallback uses 4,096 to reduce UI stalls. The actual sample count is shown with the result.
How should I read 90%, 95% and 99%?
90% means roughly 1 late morning in 10 similar mornings, 95% about 1 in 20, and 99% about 1 in 100. It is not a guarantee against weather or incidents you did not enter.
How to enter usual and longer-day times
For usual time, enter what you most often experience. For a longer day, enter a duration exceeded on about one out of ten similar days. Measuring your routine for a few days can improve confidence.
Risk drivers are comparisons, not causal shares
We compare the same virtual mornings after removing only one step's excess delay. A large change points to a possible improvement, but it does not establish how much that step contributes to actual lateness.
A recommended alarm is guidance, not a promise
The estimate covers only the duration ranges and rare delays you enter. It cannot guarantee against incidents, service outages, weather or changing habits, so add extra margin for high-stakes events.
Your data stays on your device
No account or exact destination address is required. Saved profiles stay in this browser's local storage and may disappear when browser data is cleared. Be careful with saving and JSON exports on a shared device.
Frequently asked questions
Why not just subtract preparation and travel time?
Using one fixed number hides the risk from steps that vary, such as showers and waiting. This calculator samples the variation and rare delays you enter, then shows the result as a probability.
What does 95% mean over a month?
It is roughly one late result in twenty repetitions under similar conditions. Real days differ in weather and traffic, so it does not promise an exact monthly count.
How do I enter an unreliable bus?
Use a minimum–maximum range or service interval for waiting, then add a rare delay with its chance and extra time for events such as missing a bus.
Does this include rainy days?
Only if you enter the extra time as a step or rare delay. The calculator does not fetch current weather or live traffic.
Will the result change every time?
The same numeric inputs, step structure and same sample count use the same seed and reproduce the result. Estimates may differ if your device's calculation support changes the sample count. The actual count is shown with the result.
Is my information sent to a server?
No. Calculations and profile storage happen in this browser. JSON import and export also handle the file locally on your device.