Enter a drop rate and how many drops you want. See how many attempts it takes to reach your target odds, or your chance of success after a set number of tries.
Drop rate (chance per attempt)
Attempts needed for at least 1 drop at 90% odds
Statistics at 45 attempts
Expected drops
2.3
Standard deviation
±1.5
Average attempts for 1 drop
20
Chance of 1 or more
90.06%
Chance of success by number of attempts
Horizontal axis: number of attempts.
Desired drops
Target odds
63.2% is roughly your chance after 1 ÷ drop rate attempts.
Attempts needed by number of drops
At a 5% drop rate and 90% target odds
NOTE
This calculator assumes every attempt has the same chance and attempts are independent. If your game has a pity system or odds that change as you fail, the real odds may differ from what is shown.
Distribution of drops after 45 attempts
Horizontal axis: number of drops. Centered on the expected 2.3 drops, this shows how widely real results can spread.
Simulation (Monte Carlo)
Click “Run simulation” to simulate 3,000 runs of 45 attempts each and see how much the number of drops varies.
Drop Rate Calculator: Attempts Needed for Your Target Odds
If an item drops 1% of the time, 100 attempts are not enough to be sure of one. The chance of at least one drop in n attempts is 1 − (1 − p)^n, where p is the drop rate per attempt. This calculator uses that formula, and the binomial distribution for multiple drops, to turn a drop rate into a number of attempts.
Enter the drop rate, how many drops you want, and your target odds. You get the smallest number of attempts that reaches those odds. Or switch modes: enter the attempts you plan to make and see your chance of success.
The probability curve, the distribution of drops, and the simulation show how much real results can vary around the average.
Planning farming runs, crafting, and loot rolls
Planning a farming session
Enter the drop rate and your target odds to see how many attempts to budget before you start.
Collecting several copies
Set the number of drops you need, for crafting materials or duplicates, and compare attempts for 1, 2, 3, 5, 8, and 10 drops in the quick-reference table.
Checking how your luck compares
Switch to the chance-of-success mode and enter the attempts you have already made to see how likely it was to have a drop by now.
Seeing how much results vary
Run the simulation to see how widely drops per run spread, even when every run has the same odds.
How to find the number of attempts you need
- Choose a mode: attempts needed for your target odds, or chance of success after a set number of attempts.
- Enter the drop rate as a percentage per attempt, using a preset or the custom field.
- Set the number of drops you want (1 to 50), then your target odds or your number of attempts.
- Read the result, the probability curve, and the quick-reference table. Run the simulation to compare with the calculated odds.
Note: Everything runs in your browser. Your inputs are not sent anywhere.
What these numbers do and don't tell you
- The calculator assumes every attempt has the same chance and attempts are independent. Pity systems, odds that rise after failures, and drops granted after a set number of tries are not modeled.
- Results are probabilities from the binomial distribution. Actual results vary, and a past streak does not change the odds of the next attempt.
- Use the published drop rate when the game or source gives one. Community-measured rates are estimates, and the results here are only as good as the rate you enter.
- Target odds of 99% or higher can require a very large number of attempts. 90% or 95% is a more practical planning target.
Attempts needed for one drop, by drop rate and confidence level
The smallest whole number of attempts where 1 − (1 − drop rate)^attempts reaches the target odds.
| Drop rate | 50% odds | 90% odds | 99% odds |
|---|---|---|---|
| 0.5% | 139 | 460 | 919 |
| 1% | 69 | 230 | 459 |
| 2% | 35 | 114 | 228 |
| 5% | 14 | 45 | 90 |
| 10% | 7 | 22 | 44 |
| 25% | 3 | 9 | 17 |
The table covers 1 drop. For 2 or more drops, set the number in the calculator above and check the quick-reference table next to it.
Why 1 ÷ drop rate isn't enough: the binomial math
How the calculator turns a drop rate into attempts, and why results spread out.
Rolling 1 ÷ drop rate times gets you to about 63%
At a 1% drop rate, 100 attempts leave a 36.6% chance of no drop, since 0.99^100 ≈ 0.366. As the drop rate gets small, the chance of at least one drop after 1 ÷ rate attempts approaches 63.2%. To reach 90% or 99%, you need roughly 2.3 or 4.6 times that many attempts.
How multiple drops are calculated
For k or more drops, the calculator adds up the binomial probabilities of getting 0 through k − 1 drops and subtracts the total from 1. It then searches for the smallest number of attempts where the result reaches your target odds.
Expected drops, standard deviation, and spread
Expected drops is attempts × drop rate. The standard deviation is the square root of attempts × rate × (1 − rate). At 100 attempts and a 5% rate, you expect 5 drops with a standard deviation of about 2.2, so runs with 3 drops and runs with 8 are both normal.
Independent attempts vs. pity systems
This calculator covers attempts that each have the same chance. A pity system changes the odds as you fail or caps the number of failures, so check how your game defines it before using these numbers.
Mistakes that throw off drop estimates
Assuming 1 ÷ drop rate guarantees a drop
At a 1% rate, 100 attempts still leave about a 36.6% chance of ending with nothing.
💡 See the solution▼
Budgeting for one drop when you need several
Crafting materials and duplicates need more than one drop, and the attempts needed grow with every extra copy.
💡 See the solution▼
Setting target odds too high
Asking for 99.9% odds can call for a number of attempts that is not realistic to run.
💡 See the solution▼
Treating a few reports as the real drop rate
One player getting a drop in 3 tries, or none in 50, can fall within normal variation and says little about the true rate.
💡 See the solution▼
Applying these odds to a pity system
If your game raises the odds after failures or grants a drop after a set number of tries, a constant-odds calculation does not match how the game works.
💡 See the solution▼
Questions about drop chances and attempt counts
Q.How many attempts do I need to get a drop?
A. The chance of at least one drop in n attempts is 1 − (1 − p)^n, where p is the drop rate per attempt. Pick your target odds, then solve for the smallest n that reaches them. At a 1% drop rate, that is 230 attempts for 90% odds. The calculator does this for you, and for several drops it uses the binomial distribution instead.
Q.Is 100 attempts enough for a 1% drop rate?
A. Not to be sure of it. After 100 attempts at 1%, the chance of no drop at all is about 36.6%, so the chance of at least one is about 63.4%. Rolling 1 ÷ drop rate times gets you to roughly 63%, not 100%.
Q.Can I calculate the attempts needed for more than one drop?
A. Yes. Set the number of drops from 1 to 50. The calculator finds the smallest number of attempts where the chance of getting that many or more reaches your target odds. A quick-reference table shows the result for 1, 2, 3, 5, 8, and 10 drops at your current settings.
Q.What does the simulation do, and how is it different from the calculated odds?
A. The simulation runs 3,000 simulated runs with the same number of attempts and the same drop rate, then shows how many drops each run got. Each run draws random numbers, so the result changes slightly every time and lands near the calculated odds. When the expected number of drops is above 1,000, it samples from a normal approximation of the binomial distribution to keep the page fast.
Q.Does this work with a pity system or a guaranteed drop?
A. No. The calculator assumes every attempt has the same chance and that attempts are independent. If the odds rise as you fail, or a drop is granted after a set number of tries, the real odds may differ from what is shown here.
Q.What are expected drops and standard deviation?
A. Expected drops is attempts × drop rate. Standard deviation is the square root of attempts × drop rate × (1 − drop rate), and it shows how far a typical run lands from that average. A larger standard deviation means results vary more from run to run.
Q.Can I use it outside of games?
A. Yes. It works for any repeated chance with a fixed probability, such as loot boxes, crafting rolls, critical hits, or random events. Enter the chance per attempt as the drop rate.
Q.Are my inputs sent anywhere?
A. No. All calculations and simulations run in your browser, and nothing you enter is sent to or stored on our servers.
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