What is a partial fill?
In one line: A partial fill is when only part of your order trades, because there weren't enough buyers or sellers at your price to fill all of it.
A simple example
You place a buy Limit order for 500 shares at $12.00.
Only 200 shares are for sale at $12.00 or less. They fill. Price then ticks up to $12.05 and stays there.
Your order shows: "Partially filled: 200 of 500." The other 300 shares keep waiting at $12.00.
Now you own 200 shares, not 500. If price comes back to $12.00, more may fill. If not, you'll keep 200 until you cancel the rest.
Why it happens
A Fill needs someone on the other side. At any price there's only so much waiting in the Order book. When your order is bigger than what's there, part of it trades and the rest waits.
Partial fills are common with:
- Limit orders in thin stocks or small coins.
- Big sizes compared with normal Volume.
- Quiet hours, like Pre-market and after-hours.
A Market order usually fills all the way, but it keeps taking worse prices until it does.
Why it matters
Your risk changes. Say you planned 500 shares with a $0.50 stop, so $250 of risk. With 200 shares, your risk is $100.
That's not bad. But if your stop and target were set for 500 shares, check they now match 200. Some platforms adjust attached exits automatically. Others don't.
A common mistake
Forgetting the rest of the order is still live. Hours later, price returns and the other 300 shares fill. Now you're in a bigger trade than you meant, maybe after your plan changed.
After any partial fill, decide right away: keep the rest working, or cancel it. Write that choice in your journal.
The position size calculator helps you check the risk on whatever size actually filled.
Questions
Do I pay commission twice on a partial fill?
It depends on the broker. Many charge once per order. Some charge per fill if pieces trade on different days. Check the fee schedule.
Why did my market order partially fill?
Rare, but possible in very thin markets, or with a market order that has a price protection limit. Most market orders fill fully at whatever prices are available.
Can I set an order to fill all or nothing?
Many brokers offer "all or none" or "fill or kill" options. They avoid partial fills, but they may not fill at all.
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