Tool
Paste cycle times and set the period
Little's Law: average WIP = throughput × average cycle time
Calculator Library / Software Delivery
Flow Metrics Calculator
Paste the cycle times of completed items to get throughput, percentiles for forecasting, a histogram, and what a WIP limit would do to cycle time.
Distribution
How long items take
Instructions
How to use this app
- Export the cycle time, in working days from start to done, of items completed over a period, such as the last quarter.
- Enter the number of working days the period covers, so throughput can be calculated.
- Use the percentiles to forecast: "85% of items finish within this many days".
- Try a WIP limit to see the cycle time Little's Law predicts if throughput holds steady.
- Check the longest items: they are usually blocked, and finding out why is the best investment.
What This Flow Metrics Calculator Helps You Decide
This calculator turns a list of cycle times into the measures a team needs to forecast and improve: throughput, mean and median cycle time, percentiles, and a histogram. It also applies Little's Law to show how many items are in progress on average and what a WIP limit would do to cycle time.
Use it to replace "it will take about a week" with "85% of items finish within 14 days", and to decide whether a WIP limit is worth trying.
Core Formulas
| Measure | Formula | Meaning |
|---|---|---|
| Throughput | Items completed / working days in the period | Rate of completion. |
| Percentile | The value below which that share of items fall (nearest-rank method) | The 85th percentile means 85% of items finished within that time. |
| Average WIP | Throughput × mean cycle time | Little's Law: items in progress on average. |
| Cycle time at a WIP limit | WIP limit / throughput | Predicted mean cycle time if throughput holds. |
Worked Example: 20 Items in 20 Days
The pre-loaded data are 20 cycle times from 2 to 30 days over 20 working days. Throughput is 1 item per day. The mean is 9.05 days, the median 6.5 days, the 85th percentile 14 days, and the 95th percentile 23 days. Little's Law implies about 9 items in progress, and a WIP limit of 6 would predict a mean cycle time of about 6 days, a 34% reduction.
The histogram shows the long tail: most items finish within 10 days, and three take 18 days or more. Those are worth investigating individually.
Limits and Good Practice
- Use cycle times of completed items only, measured consistently from the same start point to the same done point.
- Little's Law assumes a stable system. A team in the middle of a big change may not satisfy it.
- A WIP limit may reduce throughput if it starves a stage, so treat the prediction as a hypothesis to test.
- Avoid using these numbers to compare individuals. They describe the system.
Flow Metrics Calculator Frequently Asked Questions
How do I forecast delivery with percentiles?
Sort the cycle times of completed items and read off a percentile. The 85th percentile is the time within which 85% of items finished, so you can say a new item will usually be done within that time. It reflects your real variation, unlike an estimate for each item.
How does the calculator use Little's Law?
It divides items completed by working days to get throughput, multiplies by mean cycle time to get average work in progress, and divides a WIP limit by throughput to predict the mean cycle time with that limit if throughput stays the same.
What counts as cycle time?
The elapsed working time from when work starts on an item to when it is done. Choose clear start and done points and use them consistently. If you also want lead time, include the waiting before work starts.
Is my data stored anywhere?
No. The calculator runs in your browser and nothing is sent to a server. It does not save your entries between visits.