
Portfolio Backtesting – What You Need to Know
There’s a temptation in investing to believe that if something worked in the past, it will work again. That logic fuels many decisions, good and bad. But the real challenge lies in knowing why something worked, when it worked, and if it could work again. This is where portfolio backtesting steps in. Backtesting is like running your investment strategy through a time machine. You take a strategy using historical data and ask, “If I had done this before, how would it have turned out?” It’s a simulation that attempts to answer one of the most important questions an investor can ask: Does this idea or strategy actually work? I. What Is Portfolio Backtesting? At its core, portfolio backtesting is the process of applying an investment strategy to historical data to estimate how it might have performed in the past. While it doesn’t predict the future, it can help you better understand the strengths and weaknesses of a strategy. Think of it like test driving a new car before negotiating a price to buy it. You’re not trying to predict every traffic light, but you want to get a better idea of how it navigates through traffic. Done right, backtesting is a tool for insight. Done wrong, it creates wrongly placed confidence and expectations that are disconnected from reality. Why Backtesting Your Portfolio Matters Backtesting has become one of the foundational tools in investing. When done correctly, it helps both novice and professional investors build conviction and clarity around their strategies. It can reveal whether your approach works only in certain market conditions or holds up over long-term cycles. Without backtesting, you’re flying blind—making investment decisions based on hunches or intuition rather than evidence. But like any powerful tool, its misuse can be misleading. Too often, backtesting results are treated like sales brochures: polished, selectively edited, and overly optimistic. To benefit from the full value of backtesting, you need to understand both its utility and its limits. Reduces guesswork. Instead of relying on gut feelings, you use data to inform your investment decisions. Reveals weaknesses. Backtesting can show how a strategy behaves in bear markets or periods of volatility. Enhances discipline. If you know how a strategy has reacted over time, you’re more likely to stick with it during the tough periods. II. Key Elements of Portfolio Backtesting Backtesting isn’t just about plugging in numbers and hoping for the best. Each element of the process must be carefully considered, from the data you use to the metrics you track. A good backtest tells a story: how the strategy behaved, when it struggled, and what that might mean going forward. It is the collection of many calculations, when studied critically as a group, that starts to paint a picture of possible investment outcomes. It starts with data – accurate, comprehensive, and properly adjusted. From there, you analyze many elements of portfolio performance using the right metrics and ensure you’re testing across diverse market conditions. In this section, we break down just a few of the key components that every reliable backtest must include. 1. Historical Data Price history: Past asset prices, adjusted for splits and dividends. Trading volumes: Helps verify liquidity and buyer/seller convictions. Economic indicators: Critical for macro-sensitive strategies. Challenges: Incomplete or incorrect data can distort backtesting results. It is imperative that you have a meaningful sample size, one that is statistically sufficient. Survivorship bias can sneak in if components of the investment strategy are no longer being traded. 2. Metrics and Performance Indicators Backtesting results are only as useful as the metrics you use to analyze them. Simply seeing that a strategy made money over a certain time period isn’t enough. You need to understand how it made money, how much risk it took on, and whether that risk was justified. This is where performance indicators and metrics come into play. They allow you to compare strategies apples-to-apples, assess volatility, and gauge the potential pain points an investor might face. Whether you’re building a new portfolio or evaluating an existing one, these tools provide a language to describe both success and failure with clarity. At a minimum, some of the metrics and performance indicators you should analyze include: Compound Annual Growth Rate (CAGR): Smooths out yearly returns into a single, comparable figure. Maximum Drawdown (Daily): Tells you how far the portfolio fell from peak to trough. Don’t get lazy and look only at monthly drawdowns. This is what many in the industry use in sales literature, but it hides the amount an investment fell in the past. We have had many snapbacks in prices since 2020 that started during the month, causing a monthly number to understate the actual drop. Standard Deviation of Monthly returns (Annualized): Provides an indication of historical volatility, but because of its non-directional calculations, tends to be more suited as a longer-term measure. Rolling returns and tracking to benchmark: Shows continual rolling 12-month look back at returns instead of looking at just annual returns. Periods of extreme volatility and Bear markets don’t always fit neatly into Jan-Dec calendar. You should also track how a prior investment performed on a rolling basis, relative to an appropriate benchmark. Every model will have shorter periods when it underperformed its benchmark, but this will provide a better indication of what it has done over a more meaningful time frame. Sharpe Ratio: Provides an indication of risk-adjusted returns. Attempts to measure return per unit of risk. It is somewhat useful but has the same limitations as the standard deviation. Maximum Flat Days: Provides indication of an investments ability to recover from the drawdown. Beta: Provides an indication of how much an investment may move, in either direction, in relation to an appropriate benchmark. Ulcer Index: Provides an indication of a normal and more frequent pullback in price you may receive with an investment. Ulcer Performance Index (Martin Ratio): Concentrates on the downward drops in price in relation to the return. Attempts to measure “bang for the buck”. Distribution Outcome simulation:








