Backtrader vs Zipline: 5-Year S&P 500 Speed & Memory Test

Zipline is 3.7x Faster Than Backtrader (But You'll Hit Memory Issues First)

I ran both frameworks through a 5-year S&P 500 backtest with daily bars. Same strategy, same data, same machine. Zipline finished in 4.2 seconds. Backtrader took 15.6 seconds.

But here's the catch: Zipline's memory footprint peaked at 1.8GB while Backtracker stayed under 600MB. If you're running multiple backtests in parallel or working on a resource-constrained server, that 3x memory difference will kill you before speed matters.

This isn't a "which is better" post. It's a "here's what actually happens when you load 1,258 trading days of SPY data into each framework" post. The results surprised me, especially around how each handles indicator calculations and order execution overhead.

Photo by Christina Morillo on Pexels

The Test Setup (Because Benchmarks Without Details Are Useless)

I pulled SPY daily OHLCV data from 2018-01-02 to 2022-12-30 using yfinance — exactly 1,258 bars. Same CSV fed into both frameworks to eliminate data loading as a variable.

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