Drop Rate Probability Calculator
Fill in the values and the answer updates as you type.
How the Drop Rate Probability Calculator works
Each attempt is treated as independent with the same drop rate p. The chance of at least one drop in n attempts is 1 − (1 − p)^n, and the chance of a dry streak is (1 − p)^n. Attempts needed for a confidence level c = ln(1 − c) ÷ ln(1 − p), rounded up. The average of 1 ÷ p attempts per drop gives only about a 63% chance of success, not 100%. This does not apply to games with pity counters, guaranteed drops, or rates that rise after each failure.
Inputs and results
The Drop Rate Probability Calculator takes 3 inputs and gives 4 results.
What you enter
- Drop rate per attempt (%) — starts at 1.
- Attempts made or planned — starts at 100.
- Confidence you want (%) — starts at 90.
What you get
- Chance of at least one drop
- Chance of no drop (dry streak)
- Attempts needed for your confidence
- Average attempts per drop
Example: Drop Rate Probability Calculator with the starting values
With drop rate per attempt 1 %, attempts made or planned 100 and confidence you want 90 %, the calculator returns:
| Chance of at least one drop | 63.4% |
|---|---|
| Chance of no drop (dry streak) | 36.6% |
| Attempts needed for your confidence | 230 |
| Average attempts per drop | 100 |
Change any value above and the results update straight away.
Drop Rate Probability Calculator FAQ
How do I use the Drop Rate Probability Calculator?
Enter drop rate per attempt, attempts made or planned and confidence you want in the fields, then read chance of at least one drop, chance of no drop (dry streak), attempts needed for your confidence and average attempts per drop in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Drop Rate Probability Calculator calculate?
Chance of getting a rare drop in a number of tries, and how many tries you need. It returns chance of at least one drop, chance of no drop (dry streak), attempts needed for your confidence and average attempts per drop from the 3 values you provide.
What values does the Drop Rate Probability Calculator start with?
It opens with drop rate per attempt 1 %, attempts made or planned 100 and confidence you want 90 % so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Drop Rate Probability Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Drop Rate Probability Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.