yojoots / taxlots

Brokerage Tax Lot Processor (River)

Tax Lot Processor

Information

An important part of a brokerage product is keeping track of tax lots. A tax lot is created when a purchase is made. When a sale is made, the tax lots deducted by the sale are determined by a chosen algorithm. This processor parses a transaction log and outputs the remaining tax lots based on the chosen algorithm (fifo or hifo).

Requirements

• A modern version of Golang must be installed

Installation

git clone [email protected]:yojoots/taxlots.git
cd taxlots
go install

This will create a taxlots executable binary in your $GOBIN directory (by default $GOPATH/bin or $HOME/go/bin) which can be executed on the command-line with the taxlots command.

Alternatively, you can use go build (instead of go install) to have a taxlots binary generated in your current working directory, and either call it with ./taxlots or move it to a folder that is included in your $PATH environment variable to remove the need for the relative path prefix of ./

Implementation details

• The script takes one argument and reads a transaction log from stdin in the format of date,buy/sell,price,quantity separated by line breaks
• Transactions are expected to be provided in chronological order
• The argument passed into the script determines the tax lot selection algorithm
  • fifo - the first lots bought are the first lots sold
  • hifo - the first lots sold are the lots with the highest price
• Lots are tracked internally by an incrementing integer id starting at 1
  • Buys on the same date are aggregated into a single lot, the price is the weighted average price, the id remains the same
• After the transaction log is processed, the remaining lots (in the format of id,date,price,quantity) are printed to stdout
  • price shown with two decimal places
  • quantity shown with eight decimal places
• If an error is encountered, a descriptive error message is printed to stdout and the script exits with a non-zero exit code
• Automated tests are included in main_test.go

Testing

Unit tests can be run with go test (or go test -v if you want verbose output)

Example Usage

$ echo -e '2021-01-01,buy,10000.00,1.00000000\n2021-02-01,sell,20000.00,0.50000000' | taxlots fifo
1,2021-01-01,10000.00,0.50000000

$ echo -e '2021-01-01,buy,10000.00,1.00000000\n2021-01-02,buy,20000.00,1.00000000\n2021-02-01,sell,20000.00,1.50000000' | taxlots fifo
2,2021-01-02,20000.00,0.50000000

$ echo -e '2021-01-01,buy,10000.00,1.00000000\n2021-01-02,buy,20000.00,1.00000000\n2021-02-01,sell,20000.00,1.50000000' | taxlots hifo
1,2021-01-01,10000.00,0.50000000