OKX limit order options reviewed: Post only, IOC and FOK in day-to-day use
Most people place OKX limit orders with the default setting and never open the small options menu beside the price field. That default rests on the book until it fills or you cancel it, which suits a lot of trades. The three alternatives exist for situations where resting is not what you want: you may want to be sure you only add liquidity, or you may want an immediate result with nothing left behind. We placed small orders with each option on a liquid spot pair and recorded what happened, so the notes below are about behaviour you can repeat yourself, not about pricing.
Where the options sit and how they are labelled
On the spot trading screen choose Limit, then look for the time-in-force or advanced selector near the order form; on the app it can sit behind a small arrow or settings icon. You will see Post only, Immediate or cancel and Fill or kill alongside the default. The selection usually persists for the next order, which is the first thing to watch: after experimenting with Fill or kill, we found ourselves placing a normal order an hour later that vanished instantly because the option was still active.
Post only: useful for fee role, frustrating in fast markets
A Post only order is rejected or cancelled if it would match immediately, so anything that does fill is filled as maker. That is helpful if you are trying to keep your fills on the maker side of the fee schedule, which you can confirm on the OKX fee page for your tier. The cost is that in a moving market your order may be cancelled repeatedly because your price keeps crossing the spread. In our test, placing the price one or two ticks away from the best opposite quote worked; placing it right at the touch often did not.
IOC and FOK: immediate results, different leftovers
Immediate or cancel fills whatever it can at your limit price or better and cancels the rest, so a partial fill is normal. Fill or kill demands the whole quantity at once or nothing at all. On a deep pair with a modest size, both behaved like a capped market order. When we raised the size beyond the visible depth at our price, IOC returned a partial fill and FOK returned nothing. Check Order history afterwards: the cancelled remainder is listed, which is the quickest way to see what actually executed.
Verdict and who should bother
For casual spot buying the default is fine and the extra options mostly add ways to make mistakes. Post only earns its place for patient traders who care about the maker role and are willing to adjust prices. IOC is a practical tool for taking liquidity with a hard price limit. FOK is rarely needed by retail users, though it is handy when a partial fill would leave you with an awkward position. Whatever you choose, look at the selector before every order until checking it becomes a habit.
Risk boundary: OKX Independent Review
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Scenario checkpoint
- Open the time-in-force selector on the limit form and confirm which option is active before submitting.
- Use Post only when the maker role matters, and place the price slightly away from the touch.
- Expect partial fills with IOC and all-or-nothing outcomes with FOK.
- Review Order history after each test order to see executed and cancelled quantities.
- Reset the option to the default after experimenting so a later order does not surprise you.