You submit an order for 2 lots of EURUSD and the confirmation comes back: 1.3 lots filled at 1.0850, 0.7 lots filled at 1.0851. Nobody warned you this could happen, and now your actual position and average entry price are both slightly different from what you planned on paper. Partial fills are normal, not a malfunction, and a trader who has never seen one assumes something broke when really the market simply did not have your exact size available at one price.
Why fills split
Liquidity at any given price is finite. A limit order or a large market order can be bigger than the volume resting at the best price, so the platform fills what is available there and moves to the next price level for the remainder. This happens more on less liquid instruments and during thinner hours, and less on EURUSD during London and New York, where depth at the top of book is usually enough to absorb a retail-sized order in one clean fill. Gold and index futures during the open or close, or any pair during an off-hours window, are far more likely to split an order across two or three prices.
What a requote actually is
A requote happens when the price you clicked has already moved by the time the order reaches the venue, and instead of filling you at a worse price silently, the platform asks you to accept the new price or cancel. It is most common in fast markets, right around news releases, or with slower connections between the order request and the execution server. A requote is not a broker doing something unfair; it is a mechanism that stops you from being filled far from where you intended without your knowledge, at the cost of a brief pause while you decide.
Reading your own execution report
Every execution report is a small dataset worth actually reading instead of glancing past. It shows the requested price, the filled price or prices, the size at each, and the timestamp of the request versus the fill. Comparing requested to filled price across a month of trades on the same instrument gives an honest number for your typical slippage: maybe half a pip on EURUSD during London hours, two or three dollars on gold around the open. That number is a real cost of doing business and belongs in the same mental ledger as the spread.
Auditing your true cost of trading
Spread plus average slippage plus any partial-fill drift is the true cost of a round trip, and it is almost always higher than the quoted spread alone suggests. A trader who only tracks the spread and ignores execution quality is underestimating the cost of every single trade. Reviewing a batch of execution reports monthly, sorted by instrument and by time of day, usually reveals a pattern: certain hours or certain instruments cost noticeably more to trade than others, which is directly useful information for deciding when and what to trade at all.
What to actually do about it
Expect partial fills on larger orders in thinner instruments and size accordingly rather than assuming a clean single fill every time. Treat a requote as useful information, not an inconvenience: the price genuinely moved, and accepting a stale quote instead would have been worse. Keep execution reports and review them the same way a trading journal gets reviewed, because slippage that looks trivial per trade compounds into a real number over a hundred trades, and it is one of the few costs in trading that is fully within a trader's control to reduce.