FortuneTeller

FortuneTeller predicts your fortune. It is a personal finance simulator built and used by Harbor.

Installation

Add this line to your application's Gemfile:

gem 'fortuneteller'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fortuneteller

Usage

# Initialize FortuneTeller
sim = FortuneTeller.new(Date.today)

sim.add_primary(
  gender: :female,
  birthday: Date.new(1964, 3, 2)
)

sim.add_partner(
  gender: :male,
  birthday: Date.new(1966, 5, 5)
)

# Define primary's key events and holdings
primary_retirement = Date.new(2031, 3, 1)

primary_401k = sim.add_account(:primary) do |plan|
  plan.beginning.set(
    type: :_401k,
    balances: {
      stocks: 300_000_00,
      bonds:  200_000_00
    }
  )
end

sim.add_job(:primary) do |plan|
  plan.beginning do |p|
    p.set(
      base: 100_000_00,
    )
    p.add_savings_plan(
      percent: 7,
      match: 3,
      account: primary_401k,
      holding: :stocks
    )
  end
  plan.on(primary_retirement).stop
end

sim.add_social_security(:primary) do |plan|
  plan.on(primary_retirement).start
end

# Define partner's key events and holdings
partner_retirement = Date.new(2033, 5, 1)

partner_401k = sim.add_account(:partner) do |plan|
  plan.beginning.set(
    type: :_401k,
    balances: {
      stocks: 200_000_00
    }
  )
end

sim.add_job(:partner) do |plan|
  plan.beginning do |p|
    p.set(
      base: 75_000_00,
    )
    p.add_savings_plan(
      percent: 7,
      match: 3,
      account: partner_401k,
      holding: :stocks
    )
  end
  plan.on(partner_retirement).stop
end

sim.add_social_security(:partner) do |plan|
  plan.on(partner_retirement).start(
    pia: 1000_00
  )
end

# Start by spending the leftovers (after tax and saving) and change to
# spending an exact amount in retirement

sim.add_spending_strategy do |plan|
  plan.beginning.set(
    strategy: :remainder
  )
  future_take_home_pay = (sim.initial_take_home_pay * 0.8).round
  plan.on(primary_retirement).set(
    strategy: :exact,
    amount: future_take_home_pay # this will automatically increase with inflation
  )
end

sim.add_tax_strategy do |plan|
  plan.beginning.set(
    primary: :married_filing_jointly,
    partner: :married_filing_jointly
  )
end

# Run!
sim.simulate(
  growth_rates: {
    # these should match the holdings your retirement accounts have:
    stocks:       [1.05],
    bonds:        [1.05],

    # these are reserved parameters for the simulation:
    wage_growth:  [1.00],
    inflation:    [1.02]
  },
  # this controls the returned output. by default, the test output
  # returns all data; you can also use the MonteCarlo serializer for
  # a minimized set.
  result_serializer: FortuneTeller::ResultSerializers::Test
)

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/HarborEng/fortuneteller. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Fortuneteller project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.