It is hard to make a plan when you cannot see where the money goes. Expenses are spread across rent, food, transport, bills, and everyday spending.

Budget Buddy turns a few monthly inputs into a clear snapshot.

• Inputs: take-home income, five spending categories, and a savings goal.
• Outputs: money left after expenses, income spent, savings-goal progress, and an expense chart.
• No account linking or financial jargon; a built-in “How to use” tab explains the fields.
• A reset button restores the example values.

income <- 35000
expenses <- c(Housing = 10000, Food = 6000, Transport = 2500,
              Bills = 3000, Other = 4000)
savings_goal <- 5000
leftover <- income - sum(expenses)
spent_pct <- round(sum(expenses) / income * 100, 1)
data.frame(
  `Monthly income` = income,
  `Listed expenses` = sum(expenses),
  `Money left` = leftover,
  `Income spent (%)` = spent_pct,
  `Savings goal` = savings_goal,
  check.names = FALSE
)

##   Monthly income Listed expenses Money left Income spent (%) Savings goal
## 1          35000           25500       9500             72.9         5000

The example calculation is run when this presentation is knitted. Your live app recalculates the same kind of summary from the values a user enters.

1. UI (ui.R) collects monthly numbers and explains how to use the app.
2. Server (server.R) validates empty/negative values, totals expenses, calculates remaining money and savings-goal status, and renders a chart and a suggestion.
3. Reactive updates refresh the results when a value changes.

The app uses R Shiny and base R plotting, so it does not need a separate plotting package.

Budget Buddy is a lightweight starting point for a more intentional monthly plan.

• Change the sample amounts to match a typical month.
• Compare expense categories and notice what drives the total.
• Adjust the savings goal to see whether it fits the plan.

Run locally: place ui.R and server.R in one folder, then run shiny::runApp() from that folder.

Created: October 24, 2026