Managing the Family Budget

Family Budget Management Calculator is a financial model based on the principle of the golden ratio $\varphi \approx 1.618$ϕ≈1.618, where all budget proportions follow the 38.2 : 61.8 structure. This makes the budget self‑similar and scalable: the same distribution logic is preserved from the overall income level down to individual expense subcategories.

Budget structure

All income received by family members (total family income $W$W) is distributed according to the golden ratio rule.

38.2% → Strategic reserve (D)
This portion of income is not spent on current needs but directed to accumulation with interest capitalization. The goal of the strategic reserve is to form a source of passive income sufficient to cover current expenses $S1$S1 throughout the entire investment cycle. Investment cycles repeat over time, and their duration depends on market conditions, the capital return rate (rate $D$D), and the chosen target level of financial autonomy.

61.8% → Tactical potential
This share is intended for the family’s operational use and is further divided according to the golden ratio principle.

• 61.8% of the tactical potential (≈ 38.2% of total income W) → Current consumption (S1)
  Regular monthly expenses on food, housing, utilities, communications, transportation, and other daily family needs.
• 38.2% of the tactical potential (≈ 23.6% of total income W) → Depreciation fund (S2)
  Accumulations for repairs, major purchases, medical expenses, and other one‑time or planned costs. Unlike S1, this fund should not be fully spent by the end of the cycle; its balance at the end of the investment cycle is a target controllable parameter that can be set independently.

Thus, the budget structure is recursive: each major allocation is again divided in the same proportional ratio, making the model flexible and applicable to any income level.

Input parameters (set by the user)

The calculator operates based on the following input values entered by the user.

S1 (monthly requirement, US dollars)
The amount needed by the family to cover current monthly expenses (current consumption). This is the baseline guideline by which the model calculates the recommended income level and cycle duration.

S2 (target balance at the end of the investment cycle, US dollars)
The desired amount of funds remaining in the depreciation fund after the calculation period ends. The calculator can suggest a recommended value based on typical scenarios, but the user is free to set their own value depending on planned purchases or the risk of unforeseen expenses.

Capital rate D (% per annum)
The return (interest rate) at which the strategic reserve $D$D operates. Typically, this is the rate on deposits, savings products, or conservative investments.

S2 fund rate (% per annum)
The return on the depreciation fund assets, in most cases lower than the $D$D rate, since S2 is oriented toward higher liquidity and quick access to funds.

Output parameters

Based on the specified input parameters, the model calculates the following key output indicators.

Required family income (W, US dollars per month)
The total aggregate income at which the golden‑ratio proportions are maintained for the given S1 level. This shows the minimum income level at which the model begins to function correctly.

Investment cycle (months)
The calculated time during which the strategic reserve $D$D, replenished monthly, reaches a size sufficient to generate passive income not less than the monthly expenses S1.

Monthly withdrawal from S2 (US dollars)
The maximum permissible amount that can be withdrawn from the depreciation fund per month without risking reducing it to zero by the end of the cycle. The recommended withdrawal depends on the target S2 balance, the S2 capitalization rate, and the cycle duration.

Scenario analysis

By changing the capital rate $D$D (for example, by ±1–5%) or adjusting the target S2 balance, the user immediately sees how the timelines for reaching passive income and the final accumulated capital level shift. This allows for comparing conservative and more aggressive investment strategies.

Results visualization

The calculator provides four charts:

• budget structure by income and expense items;
• dynamics of strategic reserve $D$D accumulation and its interest income;
• changes in depreciation fund S2 and withdrawal volumes;
• progress toward the target level of financial autonomy.

The entire calculation table, charts, and explanations can be saved into a single PDF file for subsequent analysis, printing, or consultation with a financial advisor.