What is a drop rate?
A drop rate is the chance that a specific item appears on one attempt. A rate written as 1/200 is the same as 0.5%. The calculator converts every input into the same decimal probability before doing the math.
Game Probability Calculator
Drop Rate Calculator for Rare Drops and Dry Streaks
Enter any drop rate and attempt count to see your real chance of getting the item, how unlucky a dry streak is, and how many tries you need for 50%, 90%, 95%, or 99% odds.
Free Dry Calculator
Calculate your loot chance
Use a fraction like 1/500, a percentage like 0.2%, a decimal like 0.002, or just 500 for a 1 in 500 drop.
Milestones
Attempts needed for common odds
50%69attempts
63.2%100attempts
90%230attempts
95%299attempts
99%459attempts
RNG Explained
Why the listed drop rate is not a finish line
A 1 in 100 item does not mean the item appears every 100 tries. It means each attempt has a 1% chance, and the game usually starts fresh on the next roll.
What does going dry mean?
Going dry means doing many attempts without the item. If a drop is 1/500 and you reach 1,500 attempts with no drop, you are dry. The result panel explains how unusual that streak is.
How the formula works
The calculator uses P = 1 - (1 - r)^N. First it finds the chance of failing every attempt, then subtracts that number from 1 to get your chance of at least one success.
Why 100 tries is not 100%
At a 1% rate, the chance of failing one roll is 99%. Failing 100 rolls is 0.99^100, or about 36.6%. That leaves only about 63.4% chance of success after 100 attempts.
63.2%
chance at the listed rate number
The Number To Remember
At 1x the drop rate, many players are still dry
When you reach the exact drop rate number, your chance of having seen the item is only about 63.2%. For example, 512 kills on a 1/512 item gives about a 63.2% chance of at least one drop and about a 36.8% chance of still having none.
This is why the calculator also shows 90%, 95%, and 99% planning points. For a high-confidence grind, the attempt count is usually much higher than the rate printed on the wiki, tooltip, or drop table.
Planning Multipliers
How many attempts do you need?
The exact number changes with the rate, but these multipliers are useful for quick planning.
| Target | Attempts needed | What it means |
|---|---|---|
| 50% | About 0.69 x the drop rate | Half of players would have seen at least one drop. |
| 63.2% | 1 x the drop rate | The listed rate number is not a guarantee. |
| 90% | About 2.30 x the drop rate | A strong planning point for long grinds. |
| 95% | About 3 x the drop rate | Only about 1 in 20 players are still dry. |
| 99% | About 4.61 x the drop rate | Very high confidence, but still not 100%. |
Examples
Common drop rate examples
These estimates assume fixed independent attempts and no pity system.
| Drop rate | As percent | About 63% at | About 95% at |
|---|---|---|---|
| 1/10 | 10% | 10 attempts | 29 attempts |
| 1/50 | 2% | 50 attempts | 149 attempts |
| 1/100 | 1% | 100 attempts | 299 attempts |
| 1/512 | 0.195% | 512 attempts | 1,535 attempts |
| 1/1,000 | 0.1% | 1,000 attempts | 2,994 attempts |
| 1/5,000 | 0.02% | 5,000 attempts | 14,978 attempts |
Use Cases
Where this drop chance calculator works
Use it anywhere the game gives you a fixed chance per attempt. The page is universal, so it does not need to know the game name to calculate the probability.
MMO boss drops
Rare weapons, armor, pets, mounts, and raid uniques from repeated boss kills.
OSRS and RuneScape
Enter rates like 1/512, 1/1,000, or 1/5,000 and compare them with your kill count.
Roblox games
Check egg, crate, pet, and rare item odds when a game publishes the drop chance.
Diablo-style loot
Plan farming routes for rare items, legendary drops, set pieces, and run-based rewards.
Looter shooters
Estimate exotic, chest, roll, and activity reward chances across repeated attempts.
Gacha pulls
Use the base pull rate before pity or guaranteed systems change the math.
Rare encounters
Model shiny hunts, rare spawns, hidden rewards, and other low-rate events.
Game design testing
Check how a published drop rate feels across 50, 100, 1,000, or more attempts.
Important Exception
Pity systems change the math
Some games use soft pity, hard pity, bad-luck protection, duplicate protection, or guaranteed drops after a fixed number of failures. This calculator shows the base no-pity probability. If your game has pity, your real odds at high attempt counts can be better than the baseline shown here.
FAQ
Drop rate calculator questions
What is a drop rate calculator?
A drop rate calculator works out your chance of getting at least one rare item after a number of attempts. Enter the item rate and your attempts, and it shows your chance of success, your chance of still being dry, and the attempt counts needed for common confidence levels.
How do I calculate my chance of getting a rare drop?
Use the formula P = 1 - (1 - r)^N. In that formula, r is the drop rate as a decimal and N is the number of attempts. For example, a 1/200 drop rate is 0.005, and the calculator uses that value with your kill count, run count, chest count, or pull count.
What does going dry mean in games?
Going dry means doing more attempts than expected without getting the item. If a drop is 1/500 and you have 1,500 attempts with no drop, you are dry. This can feel terrible, but it is a normal part of independent RNG.
Is a 1 in 100 drop guaranteed after 100 attempts?
No. A 1 in 100 drop gives about a 63.4% chance after 100 attempts, not 100%. About 36.6% of players would still be dry at that point if every attempt is independent.
Why is the chance about 63% at the listed drop rate?
At the listed rate number, the chance settles near 63.2% because the probability of failing every attempt is still about 36.8%. That is why a 1/512 item at 512 kills is not guaranteed.
How many attempts do I need for a 90% chance?
You need about 2.3 times the drop rate number for a 90% chance. A 1/100 item needs about 230 attempts. A 1/500 item needs about 1,151 attempts. The calculator gives the exact number for your rate.
Can I use this for OSRS drops?
Yes. It works well for OSRS and RuneScape drops where each kill or reward roll uses a fixed independent chance. Enter the rate as 1/512, 1/1,000, or whatever the published rate is.
Can I use this for gacha pulls?
You can use it for base pull odds before pity. If the game has soft pity, hard pity, 50/50 protection, or a guarantee, the real odds can be higher than the base result shown here.
Does this calculator work if the game has pity?
It shows the no-pity baseline. Pity and bad-luck protection change the probability curve, so use this result as the base floor and use a dedicated pity calculator when you need exact guaranteed-pull math.
What is the formula for drop chance?
The chance of at least one drop is P = 1 - (1 - r)^N. The chance of getting nothing is (1 - r)^N. To find the attempts needed for a target probability, use N = ln(1 - target) / ln(1 - r).