# Savings goal and monthly budget calculator documentation

Inputs, formulas, assumptions and API/MCP examples for the savings goal and monthly budget calculator. Reproduce a calculation and cite its sources.

Canonical calculator: https://klarfort.com/tools/savings-goal-calculator/
Content updated: 2026-09-07
Assumptions reviewed: 2026-09-07

## Overview
Turn a savings target into a monthly amount, or enter the amount you can save to estimate the time needed. Existing savings and an assumed annual return are included in both calculations.

A separate budget mode divides entered take-home income into needs, wants and saving using 50/30/20 percentages. This is an arithmetic illustration, not a recommended allocation for your circumstances.

## How to use
1. Choose required monthly saving, months to goal or the budget illustration.
2. For a goal, enter the target, existing balance and assumed annual return.
3. Enter the deadline in months to solve for saving, or enter monthly contributions to solve for time. For budget mode, enter monthly take-home income.
4. Calculate and review the monthly amount, whole months to goal or the three budget amounts.

## Understanding the result
Required monthly saving assumes contributions at the beginning of each month. It can be zero when the existing balance and modeled return already cover the goal by the deadline.

Months to goal is the first whole month reaching the target and is zero if it is already met. An unavailable result means the target is not reached within the 600-month search.

## Questions
### Does months to goal use my entered deadline?
The duration calculation searches up to 600 months using the entered monthly contribution. The projection-month input sets the deadline for required saving and the period for the accompanying projected balance.

### What does a zero required monthly contribution mean?
Under the entered return assumption, the starting balance alone is enough to reach the goal by the deadline. It does not guarantee that a variable investment return will achieve that outcome.

### What is included in the 50/30/20 budget?
It allocates 50% of take-home income to needs, 30% to wants and 20% to saving. The calculator does not classify your expenses, assess whether that split fits your situation or move money.

## Default worked example
Monthly saving amount: 3,333.33 USD. Goal calculation with contributions at the beginning of each month. Assumptions as of 2026-09-07.

## Formula
Required monthly saving = max((goal − principal × growth^months) / (growth × annuity factor), 0). Goal duration is the first whole month reaching the target. Budget allocates income 50% needs, 30% wants, 20% saving.

- Contributions are made at the beginning of each month. Annual returns are effective rates converted to monthly compound factors. All figures use one entered currency.
- Duration searches at most 600 months and returns an unreachable state when no crossing occurs. The budget split is an arithmetic example, not a recommended spending plan.

## Inputs
- currency: Currency; default "USD"
- principal: Starting balance; default 10000
- months: Projection months; default 12
- monthlyContribution: Monthly contribution; default 0
- annualReturn: Annual return (%); default 0
- mode: Goal mode; default "required-monthly"
- goal: Savings goal; default 50000
- monthlyIncome: Monthly take-home income; default 5000

## Interfaces
Input schema: https://klarfort.com/tools/savings-goal-calculator/schema.json
Worked request and response: https://klarfort.com/tools/savings-goal-calculator/examples.json
Public table: https://klarfort.com/tools/savings-goal-calculator/table.json
JSON API: POST https://klarfort.com/tools/api/v1/savings-goal-calculator
MCP endpoint: POST https://klarfort.com/tools/mcp
MCP tool name: savings-goal-calculator

## JSON request body
```json
{
  "currency": "USD",
  "principal": 10000,
  "months": 12,
  "monthlyContribution": 0,
  "annualReturn": 0,
  "mode": "required-monthly",
  "goal": 50000,
  "monthlyIncome": 5000
}
```

## Usage and credit
Free for personal, commercial and any other lawful use with credit to KlarFort at https://klarfort.com/. Third-party data terms still apply.

Computed with KlarFort Calculators, https://klarfort.com/

Place a visible credit near the reused material or in the credits for your work or integration. One clear credit per work or integration is sufficient; no separate credit per API request is required. The credit_url field contains the homepage. The citation_url field is an optional calculator reference. Full permission: https://klarfort.com/tools/docs/license/

## Sources
KlarFort calculation methodology: https://klarfort.com/tools/methodology/ (1)