Time in force, slippage and other fine print

Every order has a price instruction (market, limit, stop) and a duration instruction: how long it stays alive. The duration is called time in force, and getting it wrong is how people end up buying a stock three weeks after they forgot about it. This lesson also nails down slippage, the difference between the price you expected and the price you got, which is the real cost of everything in this module.

Time in force

Code	Name	Meaning
DAY	Day	Lives until the end of the regular session, then cancels. The default almost everywhere.
GTC	Good till cancelled	Lives until it fills or you cancel it. Brokers usually cap this at 30-90 days.
GTD	Good till date	Lives until a date you choose.
IOC	Immediate or cancel	Fills whatever it can right now; cancels the rest. Allows partial fills.
FOK	Fill or kill	Fills the entire quantity right now or cancels the whole thing. No partials.
OPG	At the open	Participates only in the opening auction.
CLS	At the close	Participates only in the closing auction.
EXT	Extended hours	Active in pre-market and after-hours (broker-specific).

Day orders are safe by default because they clean themselves up. GTC orders are useful for patient limit entries and for protective stops you want to leave in place for a swing trade, but they carry a specific risk: you forget them. A GTC buy limit placed on an idea you abandoned can fill weeks later, on a day the stock is dropping for a very good reason. Review open orders every day you have any.

IOC and FOK are for active traders who want to grab liquidity without leaving a resting order in the book. Using a marketable limit with IOC is a clean way to say "give me what is available up to this price, then stop".

Futures have their own conventions (GTC is common and orders survive the daily session breaks), forex brokers often default to GTC, and crypto exchanges typically default to GTC and use the IOC/FOK language directly.

Slippage

Slippage is the gap between the price you expected and the price you got. It is not a fee your broker charges; it is the market charging you for wanting something immediately in a particular moment.

Sources of slippage:

The spread. You saw last at 50.01 and bought at the 50.03 ask. Two cents of slippage before anything else happens.
Walking the book. Your order was bigger than the size at the best price.
Latency. The quote you saw was a few hundred milliseconds old. The price moved between your click and your order arriving.
Stop triggers. The stop fired at 47.00, but the next bid was 46.90.
Gaps. The market closed at 49, opened at 42. Your stop at 47 filled at 42.

Slippage on a single trade is usually small. Slippage on hundreds of trades is one of the main reasons a strategy that looks profitable on a chart loses money in real life. If you ever backtest, assume slippage; if you ever trade, measure it.

Measuring your own slippage

Your journal (Module 8) should record, for every trade:

The price you intended (the price on screen when you decided).
The price you were filled.

The difference, summed across trades, is your slippage bill. It is normal for it to be roughly the spread in liquid products and much more in thin ones. If your average slippage is larger than your average profit per trade, you do not have a strategy; you have a spread donation program.

Example month	Trades	Avg slippage per share	Shares per trade	Slippage cost
Liquid large caps	40	$0.01	200	$80
Thin small caps	40	$0.06	200	$480
Options at market	40	$0.05 per contract (x100)	5 contracts	$1,000

That last row is why market orders in options are a beginner tax.

Reducing slippage

Use marketable limit orders instead of market orders.
Trade during high-volume periods (mid-morning and the last hour in US stocks; the London/New York overlap in forex).
Avoid the first minute after the open and the seconds after a scheduled news release.
Size positions relative to the displayed book, not relative to your account.
Prefer liquid products. The most reliable way to reduce slippage is to trade things that have almost none.

Key idea: Time in force decides how long your order can hurt you; slippage is how much the market charged you for immediacy. Default to day orders, review anything GTC daily, and measure slippage on every trade until it is boring.

Other fine print worth knowing

Order routing. Your broker chooses where to send your order. In the US, "smart" routing usually means sending to a market maker or venue that pays the broker (more in Module 5). You can often route directly to an exchange for a fee, which sometimes improves fills in size. Beginners can ignore this; note it exists.

Bracket / OCO orders. A bracket attaches a stop-loss and a take-profit to an entry so that when one fills, the other cancels (OCO = one cancels other). This is the single most useful order feature for a beginner because it forces you to define your exit before you enter. Most decent platforms support it.

Trade confirmations. After a fill, your broker sends a confirmation with the exact price, size, venue and fees. Read a few. They are the ground truth, and they reveal spread and slippage that the chart hides.

Try it: Find the order ticket on your (paper) platform and locate the time-in-force dropdown. Set up a bracket order: a marketable limit entry, a stop 2% below, a limit 4% above. Watch what happens when one side fills. Then, tomorrow, look at your open orders list and confirm there is nothing you have forgotten.

Recap

Time in force controls how long an order lives; day orders cancel at the close, GTC can linger for weeks.
Review open GTC orders daily so a forgotten order does not fill on a bad day.
Slippage is the difference between expected and actual price; sources include spread, book depth, latency, stop triggers and gaps.
Measure your own slippage in your journal; if it exceeds your average profit per trade, the strategy does not work.
Bracket (OCO) orders let you define stop and target at entry, which is exactly the habit a beginner needs.