Learn · Reading the tape
How price change is calculated
The same price can produce different percentages when the reference point changes.
Last updated: 2026-09-20
The arithmetic behind the percentage
Price change is the current price minus its reference price. Percentage change divides that difference by the reference price and multiplies by one hundred. In MockTradeCity, a stock moving from an 80 CC previous close to 78.40 CC has changed by negative 1.60 CC, or negative two percent. The calculation describes a relationship between two observations. It does not explain why the trades occurred or what the next execution will be.
For the City Composite, the same calculation uses index points instead of CC. Moving from 1,000 to 1,012.50 points means a 12.50-point increase and a 1.25 percent change. The percentage makes moves at different price levels comparable, while the absolute change retains the original unit. Display rounding can make a manual calculation differ slightly at the final decimal place, especially when the screen shows fewer digits than the underlying calculation uses.
Previous close means Regular close
The main daily comparison uses the preceding Regular session's close, defined by New York trading time. It does not switch to the last After-hours or Overnight execution. MockTradeCity opens on weekends too, so its previous trading day follows the city's own schedule. Applying a remembered real-exchange holiday calendar would give the wrong expectation here. For a newly listed company without a completed Regular close, the listing reference supplies the initial comparison instead.
The reference anchors the next Regular session even though trading continues between the two closes. Suppose a company finishes Regular at 100 CC, trades at 102 CC in After-hours and reaches 103 CC before the next Regular opening. If the first eligible Regular execution is 103 CC, its daily change is three percent against 100 CC. The intervening sessions help explain the path, but they do not replace the previous-close denominator.
Why two percentages can disagree
Outside Regular hours, the company page can show its completed Regular quote alongside a current session quote. The main figure still describes the Regular result relative to its own previous close. The additional line measures the extended-session price against the latest Regular close. A main reading of plus two percent and a Pre-market reading of minus half a percent therefore need not conflict. They cover different intervals with different starting prices.
For a numerical version, let the older close be 100 CC and the latest Regular close be 102 CC. The main completed-session move is plus two percent. If Pre-market then trades at 101.49 CC, the new session is down half a percent from 102 CC. That price is still above 100 CC. Both percentages can be correct, and neither can be interpreted fully without the price it uses as its base.
Other screens use other starting points
The Market's short-interval ranking compares a recent Regular price with the price five minutes earlier. It answers a narrower question than the daily ranking. Chart views also identify their own baseline: Regular and all-session intraday views use previous close, while extended-session views refer to the Regular close. A multi-day view can compare with its first point. The label beside a percentage is part of the measurement, not optional decoration.
Your position's P&L is based on your own entry cost rather than yesterday's close. A stock can rise today while your position remains below its purchase cost, or decline today while remaining above it. For example, a purchase at 110 CC is still below cost when the latest price reaches 105 CC, even if previous close was 100 CC. Daily market movement and the outcome of a particular account's trade answer different questions.
Where to compare changes in the city
The company page provides the main change next to its quote and a separate labeled line for extended-session data. The Market and Watchlist mobile views can switch supported change displays between percentage and absolute amount. The Composite card shows points and percentage together. Reading those alongside previous close makes the arithmetic visible. None of the display choices changes your holdings or creates a new trade; they simply select a presentation of existing data.
Daily Wrap fixes the comparison to a completed day and places the Composite's close, previous close and change together. Account supplies position-level P&L for comparison with your own cost. When two figures seem inconsistent, identifying their session, reference and unit usually explains the difference. All company prices and account amounts here are fictional City Coin; the index is expressed in points. A percentage alone does not identify which of those measurements you are looking at.