Trading guide
14 min
How the matching engine treats your orders, what each order type does, what you pay, and how to stay in the game long enough to get good at it.
How matching works
Price-time priority
The best price trades first; at the same price, the order that arrived first trades first. Everyone sees the same book and is matched by the same rule.
Maker and taker
An order that rests on the book is a maker. An order that trades against it is the taker. The fee follows the role, not the side: a resting sell that gets bought pays the maker fee.
A trade is settled in the same database transaction that matches it: both sides' balances move together or not at all.
Order types
| Type | What it does | Use it when |
|---|---|---|
| Limit | Trades at your price or better; the rest waits on the book | You care about price more than speed |
| Limit, post only | Only ever rests; refused if it would trade at once | You want the maker fee, guaranteed |
| Market | Trades now against the best prices, inside a 5% band; the rest is cancelled | You care about speed more than price |
The 5% band
A market order cannot fill more than 5% away from the best price at the moment it arrives. One stray offer far from the market cannot fill you at an absurd price.
Fees
| Role | Rate at the time of writing | Charged in |
|---|---|---|
| Maker | 0.10% | The asset you receive |
| Taker | 0.20% | The asset you receive |
Example — a resting sell that fills
Sell 0.05 BTC at 80,000, resting (maker). Proceeds 4,000.00 USDT Maker fee 0.10% 4.00 USDT You receive 3,996.00 USDT
Prices and sizes
Tick size
The smallest price step. A price that is not a multiple of it is refused. On BTC/USDT at the time of writing: 0.01 USDT.
Lot size and minimum
The smallest amount step, and the smallest order. On BTC/USDT at the time of writing: lot 0.00000001 BTC (one satoshi), minimum 0.00001 BTC.
The venue refuses an order that breaks these rules rather than rounding it for you — a silently rounded order is an order you did not place.
Slippage and depth
The top of the book is a price for its size, not for yours. A large order walks down the book, filling each level in turn, and its average price is worse than the first one.
Example — walking the book
Asks: 0.10 BTC @ 80,000
0.20 BTC @ 80,050
0.50 BTC @ 80,200
Market buy 0.30 BTC:
0.10 × 80,000 = 8,000
0.20 × 80,050 = 16,010
average 80,033 — 33 above the best askHabit worth having
Before a large order, read the Sum column. If your size is a large share of the depth, split it, or use limit orders.
Managing risk
- 1Size each position so that losing half of it would not change your life.
- 2Never trade with money you need, or money you borrowed.
- 3Decide in advance what would make you sell, and write it down.
- 4Keep long-term holdings in a wallet you control, not on any exchange — ours included.
- 5Assume any message that hurries you is an attack.
Nothing here is advice
OpeniBank is not a licensed adviser. These are habits, not recommendations about what to buy or when.
What you should take away
- Orders match by price, then by time; fees follow the maker or taker role.
- Post only guarantees a resting order; market orders are bounded by a 5% band.
- Tick, lot and minimum are enforced, never rounded.
- Depth decides what a large order really costs.