# 50/30/20 Budget Calculator

> Splits monthly after-tax income into needs, wants and savings/debt repayment with the 50/30/20 rule (Warren & Tyagi, All Your Worth, 2005) or custom percentages, and compares the targets with current spending when it is given.

- Calculator id: `budget-50-30-20` · Category: Finance (`finance`) · Tool name: `calculate_50_30_20_budget`
- Canonical page: https://tttkmbb.com/finance/budget-50-30-20 · This document: https://tttkmbb.com/finance/budget-50-30-20.md · JSON definition: https://tttkmbb.com/finance/budget-50-30-20.json

## Purpose

Splits monthly after-tax income into needs, wants and savings/debt repayment with the 50/30/20 rule (Warren & Tyagi, All Your Worth, 2005) or custom percentages, and compares the targets with current spending when it is given.

**Use when:** You want target amounts for essentials, discretionary spending and savings from take-home pay, or to check how far current spending deviates from the 50/30/20 split.

**Do not use when:** You need the time or deposit to reach a savings target (use savings-goal), a debt payoff schedule (use debt-payoff), or a line-item budget. Informational; not financial advice.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `monthly_after_tax_income` | number |  | required | Take-home pay per month after income tax and payroll deductions (add back retirement contributions withheld at source if you count them as savings). (> 0, max 1000000000) |
| `needs_percent` | number | % | optional, default 50 | Share for essentials: housing, utilities, groceries, insurance, minimum debt payments, transport to work. (min 0, max 100) |
| `wants_percent` | number | % | optional, default 30 | Share for discretionary spending: dining out, entertainment, travel, subscriptions. (min 0, max 100) |
| `savings_percent` | number | % | optional, default 20 | Share for savings, investments and debt repayment beyond the minimums. The three shares must sum to 100. (min 0, max 100) |
| `current_needs` | number |  | optional | What you currently spend on needs per month, for comparison. (min 0, max 1000000000) |
| `current_wants` | number |  | optional | Current monthly discretionary spending. (min 0, max 1000000000) |
| `current_savings` | number |  | optional | Current monthly savings and extra debt repayment. (min 0, max 1000000000) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `needs_budget` | number |  | monthly_after_tax_income × needs_percent / 100. |
| `wants_budget` | number |  | monthly_after_tax_income × wants_percent / 100. |
| `savings_budget` | number |  | monthly_after_tax_income × savings_percent / 100. |
| `annual_savings` | number |  | savings_budget × 12. |
| `needs_difference` | number |  | needs_budget − current_needs (positive = under budget; only when current_needs is given). |
| `wants_difference` | number |  | wants_budget − current_wants (positive = under budget; only when current_wants is given). |
| `savings_difference` | number |  | savings_budget − current_savings (positive = saving less than the target, i.e. a shortfall; only when current_savings is given). |
| `current_needs_percent` | number | % | current_needs / income × 100 (when given). |
| `current_wants_percent` | number | % | current_wants / income × 100 (when given). |
| `current_savings_percent` | number | % | current_savings / income × 100 (when given). |
| `assessment` | string |  | Plain-language comparison of current spending with the targets. |

## Formula

`needs_budget = income × needs_percent/100; wants_budget = income × wants_percent/100; savings_budget = income × savings_percent/100; annual_savings = savings_budget × 12; x_difference = x_budget − current_x; current_x_percent = current_x / income × 100`

The 50/30/20 rule from Warren & Tyagi's All Your Worth (2005) applies to after-tax income and treats minimum debt payments as needs and extra repayments as savings; it is a rule of thumb, not a prescription, and custom percentages (e.g. 60/20/20 in high-cost cities) are accepted as long as they sum to 100.

## Data Sources

- Warren E. & Tyagi A. W. (2005) All Your Worth: The Ultimate Lifetime Money Plan, Free Press — https://www.simonandschuster.com/books/All-Your-Worth/Elizabeth-Warren/A-Guide-to-Personal-Finances/9780743269889 (textbook, retrieved 2026-09-24)
- Investopedia – The 50/30/20 Budget Rule Explained With Examples — https://www.investopedia.com/ask/answers/022916/what-502030-budget-rule.asp (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/budget-50-30-20?monthly_after_tax_income=…`
- `POST https://tttkmbb.com/api/v1/calculate/budget-50-30-20` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/budget-50-30-20 · OpenAPI operationId `calculate_50_30_20_budget` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "budget-50-30-20", "inputs": {…}}`

## Example

- 4,000 take-home per month, default 50/30/20: inputs `{"monthly_after_tax_income":4000}` → `{"needs_budget":2000,"wants_budget":1200,"savings_budget":800,"annual_savings":9600}`
- 6,500 per month, currently spending 3,500 / 1,800 and saving 1,200: inputs `{"monthly_after_tax_income":6500,"current_needs":3500,"current_wants":1800,"current_savings":1200}` → `{"needs_budget":3250,"wants_budget":1950,"savings_budget":1300,"annual_savings":15600,"needs_difference":-250,"wants_difference":150,"savings_difference":100,"current_needs_percent":53.85}`

```
GET https://tttkmbb.com/api/v1/calculate/budget-50-30-20?monthly_after_tax_income=4000
```

## Limitations

You need the time or deposit to reach a savings target (use savings-goal), a debt payoff schedule (use debt-payoff), or a line-item budget. Informational; not financial advice. The 50/30/20 rule from Warren & Tyagi's All Your Worth (2005) applies to after-tax income and treats minimum debt payments as needs and extra repayments as savings; it is a rule of thumb, not a prescription, and custom percentages (e.g. 60/20/20 in high-cost cities) are accepted as long as they sum to 100. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Is the income before or after tax?**

After tax (take-home pay). The rule was defined on after-tax income; if retirement contributions are deducted from your paycheck before you see it, add them back to income and count them as savings.

**Where do debt payments go?**

Minimum required payments are needs (they are not optional); anything paid above the minimum counts toward the 20 % savings/debt-repayment share.

**What if my needs exceed 50 %?**

Common where housing is expensive. Adjust the shares (e.g. 60/20/20) to keep the savings share, or treat the excess as a signal to lower fixed costs; the rule is a guideline, not a requirement.

## Related

- [Savings Goal Calculator](https://tttkmbb.com/finance/savings-goal.md) — Turn the savings target into a timeline for a specific goal.
- [Debt Payoff Calculator](https://tttkmbb.com/finance/debt-payoff.md) — Apply the savings share to clear a balance faster.
- [Salary Converter](https://tttkmbb.com/finance/salary-converter.md) — Convert an annual salary into monthly pay before budgeting.