How MT5 Orders Are Calculated

Direct answer

In MetaTrader 5 (MT5), “order calculation” usually means computing the values needed to place an order—most importantly the target price (or trigger level) and the expected trade volume (position size)—based on inputs such as an instrument’s contract specifications and the order’s parameters (order type, lot size, and price fields). The exact numeric result is therefore not a single universal formula; it is a small set of mechanics that combine inputs from the order request and the instrument settings, then are finalized by the execution engine when the order is filled.

Because you asked for how MT5 Orders are calculated, the most verifiable way to describe it is as a process:

1. decide the order type and its price/trigger fields,
2. resolve the requested price into an executable price using the market quote model assumed at the moment of execution,
3. convert the chosen volume (lots) into the position’s notional exposure using the instrument’s contract specification,
4. compute the economic quantities (e.g., profit/loss) later from the realized fill price.

Mechanics and definitions

Order price vs order trigger

MT5 orders typically fall into categories such as market execution (immediate) and pending/trigger-based execution (future condition). The key difference for “calculation” is what the platform uses as the operative price input:

• Market order: the “calculation” is largely the selection of the executable fill price at execution time.
• Pending order: you calculate relative to a trigger level (e.g., a target price). The order becomes eligible when the market reaches that condition.

Common inputs that affect the computed result

An order request normally includes:

• Order type (market or pending/trigger-based).
• Requested price fields (for market, this is usually not a fixed target; for pending, it is an explicit level).
• Volume (often expressed as lots).
• Instrument selection (symbol). The symbol ties the order to contract settings.
• Execution and account settings (e.g., whether commissions are charged and how they are applied).

To compute consistent numbers, MT5 also needs instrument configuration such as:

• Contract size / units per lot: how many underlying units one standard lot represents.
• Tick size and tick value (or equivalent pricing granularity): used to define how prices move in discrete steps and how value changes with price moves.
• Minimum/step volume: used to round the requested lot size to permitted increments.

A practical “formula set” you can check

While MT5’s internal implementation details are not identical for every broker setup, a generic and checkable model is:

1. Normalize volume to permitted steps

   • Let V_req be the requested lots.
   • Let V_min be the minimum lot and V_step be the lot step.
   • The platform effectively uses a normalized volume V_used that satisfies the step rules (rounding or rejection can occur depending on implementation).

2. Convert lots to underlying exposure

   • Let C be the contract size (units per 1 lot).
   • Let U = V_used × C be the notional units used for later profit/loss calculations.

3. Determine fill price at execution time

   • Market execution uses a realized fill price based on the current quote and execution model.
   • Pending execution uses the first price that satisfies the trigger condition and then the realized fill price.

4. Compute P/L from the realized fill price (later)

   • Profit/loss depends on the price difference between entry and exit. The “value per price unit” is governed by tick value or equivalent contract settings.

Even if you never see the internal MT5 code, these are the inputs and relationships that make the outcome reproducible when you know the instrument settings and the realized fill price.

Evidence or example (with explicit assumptions)

Assume a simple educational model (not broker-specific) to illustrate what “calculated” means.

Example A: Market order sizing and exposure

Assumptions (you must supply these from your environment):

• You place a market order on symbol X.
• Requested volume is V_req = 0.20 lots.
• Symbol X contract size is C = 100,000 units per lot.
• The platform allows 0.01 lot steps and does not reject 0.20.

Step-by-step check:

1. Normalize volume: V_used = 0.20 (no rounding needed under the step assumption).
2. Convert to units: U = V_used × C = 0.20 × 100,000 = 20,000 units.

At this stage, “order calculation” for exposure is complete because it only used order volume and instrument settings. The later profit/loss will use the realized fill price.

Example B: Pending order trigger vs fill

Assume you place a pending order with a trigger level P_trigger. The calculation is:

• The system waits until market price satisfies the trigger condition.
• When it triggers, the executed fill price may be worse than P_trigger due to execution dynamics.

So the checkable difference is:

• Trigger price affects eligibility.
• Fill price affects realized outcomes.

This separation is the most common reason people find that “my calculated expectation did not match the result.”

Limitations and risks (what can break the calculation)

1. Spread and quote changes at execution time Even if you compute a target number, the realized fill uses the market state at execution. If the bid/ask or last-traded price shifts between your calculation and fill, your realized result can differ.

2. Slippage and partial fills In fast markets, the executable price can move past what the platform displayed at the moment you prepared the order. Depending on the broker’s execution model, fills can also be split.

3. Rounding and validation of volume Requested lot sizes may be rounded to permitted increments or rejected. If your “calculation” assumes the exact requested volume, it may not match what was actually used.

4. Costs applied in execution/account settings Commissions, swap/rollover behavior, and other fees can change the net economic result compared with any calculation that ignores them.

5. Historical relationships do not guarantee future results Even if you have prior fills for the same symbol and volume, you cannot assume the same spread behavior, fill prices, or costs will occur later.

Verification and what to check next

To independently verify “how MT5 Orders are calculated” in your case, gather only stable, checkable inputs from your own environment:

• The symbol’s contract specifications (contract size/units per lot, tick size/value, volume minimum/step). - The order type you used (market vs pending/trigger). - The requested volume and whether any normalization/rounding occurred. - The realized fill price(s) shown in the trade/execution history.