Partial Fills
A partial fill happens when only part of your order executes. The remaining quantity stays open (pending) or is cancelled, depending on your order settings and the market’s available liquidity.
In plain English: “I asked for 10 units, but only 6 were available right now.”
Quick Navigation
Partial fills are normal in real markets. The key is understanding when they matter and how to manage them.
Why Partial Fills Happen
Markets are built on available liquidity at each price level. If your order size is bigger than what’s available at your price, it may fill in pieces.
- Limited liquidity at the price: not enough buyers/sellers at that level.
- Fast markets: liquidity changes rapidly (especially around news).
- Order type: limit orders can fill partially at the limit price; market orders can fill across multiple price levels (“walking the book”).
- Venue rules: some venues allow partial fills by default; others depend on time-in-force settings (e.g., IOC/FOK).
OTC vs exchange note
On exchange-traded markets, partial fills are visible because the order book is real. In OTC products (like many CFDs), the broker may internalise or source liquidity from providers — which can change how partial fills appear.
How Partial Fills Affect Your Trade
Partial fills can change execution quality and trade management:
- Different average price: fills at multiple prices create an average entry/exit price.
- Position size mismatch: you may end up smaller than planned, affecting risk and reward.
- Stop-loss and take-profit sizing: attached orders may need to match the filled size.
- Extra commissions/fees: multiple fills can sometimes mean multiple charges (depends on broker/venue).
For small retail sizes on liquid instruments, partial fills are often rare. They become more common in thin markets, large size, or high volatility.
Average Price (VWAP) Explained
When an order fills in parts at different prices, your platform typically shows a single average entry/exit price. This is usually a volume-weighted average price (VWAP).
VWAP idea (simplified)
Average Price = (Fill1Price × Fill1Size + Fill2Price × Fill2Size + …) ÷ (Total Size)
This ensures bigger fills influence the average more than smaller fills.
Why VWAP matters
Your stop-loss distance, risk per trade, and performance metrics are based on the average price. If you ignore this, your risk calculations can be wrong.
Example: Partial Fill on a Limit Buy
You place a buy limit for 1,000 shares at £10.00. At £10.00, only 400 shares are available immediately.
- You get filled for 400 shares at £10.00.
- The remaining 600 shares stay pending (unless you used IOC/FOK).
- If more liquidity appears at £10.00, the rest may fill later.
- If price moves away, the remaining shares may never fill.
Result: you have a smaller position than planned, which changes your risk and target calculations.
How to Reduce Partial Fills
Partial fills are not always “bad”, but if you want fewer of them:
- Trade liquid markets: major FX pairs, large indices, high-volume shares.
- Reduce order size: smaller orders are easier to fill at one price level.
- Use limit orders: control the maximum/minimum price (but accept no-fill risk).
- Avoid volatile windows: major news releases, open/close, low-liquidity sessions.
- Consider IOC/FOK: where available, they control whether partial fills are allowed.
- Split orders deliberately: if you want to scale in, do it intentionally with a plan.
Beginner-friendly rule
If your strategy depends on exact size and price, avoid trading during high volatility and keep sizes modest until you understand your platform’s execution behaviour.
Common Misconceptions
-
“Partial fills mean something is wrong.”
Not necessarily. They are a normal result of limited liquidity and fast-moving prices. -
“If I use a market order, I’ll always get filled instantly in full.”
Market orders prioritise execution, but large orders can still fill across multiple levels, creating partial/segmented fills and a worse average price. -
“My stop-loss and take-profit will always auto-adjust.”
Some platforms adjust attached orders automatically; others require manual confirmation. Always check your position and order sizes after a partial fill.
✅ Quick Checkpoint
Try answering before expanding the model answers.
1) What causes a partial fill?
Not enough liquidity available for your full size at your price (or during your execution window).
2) How does a platform usually display multiple fills?
As one position with an average (volume-weighted) entry/exit price.
3) Name two ways to reduce partial fills.
Trade more liquid instruments, reduce order size, avoid volatile periods, or use IOC/FOK where available.
If you can explain these points, you understand why partial fills occur and how to manage them sensibly.
Frequently Asked Questions: Partial Fills
Are partial fills more common with limit orders or market orders?
They can happen with both. Limit orders may partially fill at the limit price if limited size is available there. Market orders can fill across multiple price levels, which can also appear as multiple fills.
Do partial fills increase trading costs?
Sometimes. On some venues/brokers, multiple fills can mean multiple commission charges or slightly different fees. On others, costs are aggregated. Check your broker’s fee model.
What should I do if my order partially fills?
First, confirm your actual position size and average price. Then check your stop-loss and take-profit sizes. Finally, decide whether to leave the remainder working, amend it, or cancel it.
Can I prevent partial fills completely?
Not always. You can reduce the likelihood by trading liquid markets and sizing appropriately. On some venues you can use FOK to prevent partial fills, but that increases no-fill risk.