OHLC / OHLCV Data
Also known as: OHLC, candle data, bar data, price bars, open high low close
What is it?
OHLC data is the four numbers that summarise one candle: the open, the high, the low and the close for that interval. Add traded volume and it becomes OHLCV, the standard row format every chart, backtest and bot reads. One row is a compression of everything that happened in the period. A 15-minute EUR/USD candle reading open 1.0850, high 1.0868, low 1.0846, close 1.0864 tells you the range was 22 pips, the net move was 14 pips upward, and buyers finished near the top.
What it cannot tell you is the order those prices occurred in. That same candle is consistent with a rise to the high and a drift back, or a fall to the low first and a sharp recovery. That missing sequence is the source of a specific and expensive backtesting error. If a strategy's stop sits at 1.0846 and its target at 1.0868, both were touched inside this one candle, and a tester working only from OHLC has to guess which came first.
Guessing favourably turns a losing strategy into a profitable-looking one. It is why serious testing uses tick data or a lower-timeframe series for the inside of each bar, and why a backtest that never says how it resolved this deserves suspicion.
Why it matters: OHLC is the standard price row every bot and backtest reads, but it discards the order prices occurred in, which is where the most flattering backtest errors hide.
Range = high - low; body = |close - open|; upper wick = high - max(open, close)
When a bar contains both the stop and the target, a tester working from OHLC alone has to assume which was hit first, and the wrong assumption inflates the result.
Real-world example
A strategy showing a 1.42 profit factor on OHLC bars fell to 0.93 when retested on tick data, because 18 percent of its trades had both the stop and the target inside a single bar.
How SignalBots handles it
SignalBots signals name an entry, a stop and a target as explicit prices rather than as bar conditions, so the levels do not depend on how a tester resolved the inside of a candle. See /risk-warning.
Pro tip
Before trusting a backtest, count how many trades had both the stop and the target inside one bar. If that share is more than a few percent, the result is an assumption, not a measurement.
Common pitfalls
Assuming a green candle means price rose steadily, when the same close can follow a deep intrabar fall that would have taken out a stop on the way.
Frequently asked questions
What does the V in OHLCV add?
Traded volume for the interval. In centralised markets it is a true count; in spot forex, which has no central exchange, most feeds report tick volume, meaning the number of price updates rather than the amount traded.
Why is the open sometimes different from the previous close?
That difference is a gap, and it happens when the market moves while it was closed, such as over a weekend or between sessions. In continuously traded markets the open normally matches the previous close very closely.
Is OHLC enough to backtest a strategy?
For strategies acting on the close of a bar, usually yes. For anything with a stop and target that can both be reached inside one bar, you need tick data or a lower-timeframe series, or the result depends on an assumption.
Do different brokers report different OHLC values?
Yes, slightly. Spot forex has no single consolidated feed, so each broker's high, low and close reflect their own quotes and session boundaries. Small differences at the extremes can decide whether a stop was touched.
What is tick data and when do I need it?
It is every individual price update rather than a per-interval summary. Use it when the inside of the bar matters, meaning stop-and-target strategies, scalping, and anything where the fill price rather than the bar's direction decides the result. Your capital is at risk.
Trading involves substantial risk of loss. Historical and backtested results do not guarantee future performance. Read the full risk warning.
