I'm new to this so my apologies if this is out of place or not a "correct" use of backtesting.

Is there a free service (or python package) for backtesting investment strategies for Vanguard mutual funds?

I have an automatic investment that occurs monthly but I'm curious how it would have improved (or not) over the past 12 months if I had contributed every 2 weeks instead of once per month.

As an example with fake numbers, what would the difference be over the past 12 months between contributing $1000 every month versus $500 every 2 weeks to VFINX?

  • Have you tried pulling data from the usual sources? Yahoo or Google? And then a simple spread sheet? Commented Jun 3, 2017 at 14:41
  • 1
    I pulled the data for 2016 from Yahoo and used a spreadsheet to manually calculate the differences (without accounting for dividends). It looks like the Python backtrader module will make the process a bit more repeatable.
    – devteam
    Commented Jun 4, 2017 at 19:08
  • You might want to check out Quantopian.
    – Jack Moody
    Commented Oct 22, 2018 at 1:52

1 Answer 1


I've been using https://www.portfoliovisualizer.com/backtest-portfolio

In the few cases I've manually tested it out using code, it seems to be accurate..

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