OHLC Candlesticks: Read the Bar Without Inventing the Price Path

Four values and a defined interval

Open is the interval's first price in the selected series; close is its last available price. High and low are the extremes between them. The bar's timestamp convention matters: a label may identify the start of the period rather than the time of its closing price. For example, MetaQuotes documents the time field in MqlRates as the period start.

A candle body spans the open and close. Its upper and lower wicks extend to the high and low. Colors are presentation settings, so read the values rather than assuming that a particular color always means an increase.

Calculate one candle

Suppose a completed bar has open 100, high 104, low 98 and close 102. The following distances are in the instrument's quoted price units, not automatically in dollars:

Geometry of a hypothetical OHLC bar

Measure	Calculation	Distance
Full range	104 − 98	6
Body	|102 − 100|	2
Upper wick	104 − max(100, 102)	2
Lower wick	min(100, 102) − 98	2

The close is two price units above the open. That observation does not establish a profitable trade: an entry could have occurred elsewhere, the position could have been short, and executable bid or ask prices may differ from the chart series.

The sequence that the candle hides

Both 100 → 104 → 98 → 102 and 100 → 98 → 104 → 102 produce those same four values. Imagine an existing long position with a stop at 99 and a target at 103. In the first path, 103 is crossed before 99; in the second, 99 is crossed first. A backtest that sees only this bar cannot recover which path actually occurred.

This matters when a simulation fills several orders inside one interval. Choosing the favorable sequence without evidence inflates the result. A conservative assumption, a clearly described uncertainty rule, or appropriate finer data is needed. Even tick data must represent the relevant quote side and execution rules; more rows do not by themselves guarantee a realistic fill model.

Validate the series before diagnosing an order

Record instrument identity, timeframe, timezone, session and price type. A bid candle reaching a price does not necessarily show that the ask reached it at the same moment. For market orders, the last traded price also need not be the executable price, a distinction explained in Investor.gov's order guide.

Check whether the final candle is still forming and whether any periods are missing. Transformed charts can use calculated values rather than actual transaction prices, so their displayed open and close need separate interpretation.

Use the chart to locate a period of interest, then inspect order and execution records for acceptance, trigger and fill evidence. The related bid–ask reference and volume-field comparison cover two other common reasons that visually similar bars describe different data.