How Equity Replay Calculates a Historical Portfolio Replay

Equity Replay answers one narrow question: If this allocation had been set at the start of a historical window, how would the mix have moved through that window?

It is a what-if replay, not a brokerage account and not a prediction. You choose the positions and percentages, then review a chart built from historical close prices.

The inputs

Every replay has four inputs:

• A list of stock symbols.
• A percentage weight for each symbol. The total must equal 100%.
• A historical range, such as one month, six months, five years, or ten years.
• An illustrative starting value, such as $10,000.

The starting value changes the dollar display. It does not change the percentage movement of the portfolio.

How the chart is calculated

First, each stock’s historical series is aligned to the dates shared by all selected holdings. Each series is rebased to 100 on the first shared date. A 10% position therefore contributes 10% of its rebased movement, while a 50% position contributes 50%.

Those weighted movements are combined into one portfolio index. The index is then translated into the illustrative starting value shown above the chart. The chart’s “Historical change” is the movement from the first shared date to the last date.

What “no rebalancing” means here

The allocation is applied once at the start of the replay. Equity Replay does not add money, remove money, trade between positions, or reset the percentages during the window. It also does not label the result as a buy-and-hold account. It is simply a single-start allocation mapped across historical prices.

What is left out

The replay uses close-price movement and excludes dividends, fees, taxes, deposits, withdrawals, execution, and future projections. A dashed SPY line may appear as a reference, but it is not part of your allocation.

Read the date range and methodology note before comparing two results. Then build a portfolio or continue with how to create a what-if stock portfolio with percentages.