Budgeting V1

[zachgoll]

This PR introduces a basic budgeting module along with some updates to categorization of transactions.

Transfers and Payments

One of the major goals of this app is to treat "transfers" and "payments" as first-class citizens rather than a categorical afterthought. Most personal finance apps leave it to the user to identify transfers and payments, which generally ends in the user asking, "How do I incorporate transfers in my budget and goals?". This leads to inaccurate calculations of spending, income, and overall budgets because the app does not give the user a clear way to separate these concepts from expenses and income (the primary purpose of budgeting). Our goal is to give transfers/payments a clear "home" in the app and assist the user in identifying them. Below are some technical definitions of each:

• Transfer - any transaction that is simply a compositional shift of wealth. A transfer does NOT affect a users net worth because it is simply a movement from one of their accounts to another.
  • Example: User moves $5,000 from a checking account (asset) to a Brokerage account (asset), which does not affect net worth, but changes the composition of the user's balance sheet.
• Payment - a payment is a specific type of transfer where a user makes a transfer from an asset account to a liability account, therefore reducing debt.
  • Example: User moves $2,000 from a checking account (asset) to a Credit card account (liability), which reduces both account values, but does NOT change net worth.

Transfer/Payment treatment

Transfers and payments are incorporated into a user's budget based on the classification of account in which they correspond to.

• All transfers are excluded from budgets since they are neither "spending" nor "income"
• Payments made to/from credit card accounts are excluded from budgets to avoid "double counting"
  • Since all the credit card account transactions will be categorized and summed up, we need to exclude the monthly payment made from the user's Checking account to avoid double counting. A credit card is a "Suspense" or "Clearing" account that acts as a temporary holding area for categorized transactions that will eventually be cleared by the debt servicing payment.
• Payments made to loan accounts are included in budgets, because this is a monthly "expense" that a user must budget for

Transfer identification

One of the biggest challenges when dealing with transfers is identifying them. Our app can identify 90% of transfers by looking at the amount, account, and date. Two transactions with opposite amounts, within a few days of each other from different accounts give high confidence that we're dealing with a transfer.

That said, there are always edge cases. The most notable one is where the user has made a transfer to an account that does not exist in Maybe yet, or one that is being tracked by value only and doesn't have a corresponding transaction. In this case, we must rely on the user to tell us that this was a transfer.

[zachgoll]

Will open new PR for this. #1585 covers a good portion of the changes here.