Equal amounts can be unequal burdens
The same dollar amount consumes different fractions of income.
Shared planning
Couple Budget Scenario Calculator
Compare equal, income-proportional, and protected-capacity contribution policies with retained income for both partners.
CONTRIBUTION POLICY COMPARISON
Compare three rules without calling one of them automatically fair
The same shared need can be divided equally, by total-income weights, or by income left after protected amounts. The table preserves both contributions and retained income so the rule’s effect stays visible.
Equal-policy A contribution-
Income-policy A contribution-
Capacity-policy A contribution-
Capacity-policy B contribution-
Largest minimum retained income-
CONTRIBUTION POLICY COMPARISON
Three-policy retained-income comparison
“Largest minimum retained income” is one descriptive metric, not a fairness verdict. The choice of protections, needs, bargaining power, debt, care work, and ownership may matter more than that ranking.
| Policy | Partner A contribution | Partner B contribution | A retained income | B retained income |
|---|
DETAILED CALCULATION PROCESS
Formula, symbols, defaults, conversions, live substitution, and reconciliation
1. General symbolic formula
Equal: C_i=N/2; Income: C_i=N×I_i/ΣI; Capacity: C_i=N×(I_i-P_i)/Σ(I-P)
2. Calculation logic
Apply the same shared need to three separate weighting systems. Equal ignores income; income-proportional uses full income; capacity-weighted subtracts protected amounts first. Retained income is income minus contribution.
3–4. Symbol names, meanings, and units
| Symbol | Meaning | Unit |
|---|---|---|
| N | Shared need | USD/month |
| I_i | Partner i income | USD/month |
| P_i | Partner i protected amount | USD/month |
| C_i | Policy contribution | USD/month |
| R_i | Income retained after contribution | USD/month |
| Σ | Sum across both partners | — |
5. Default inputs
- Total shared monthly need: 3600
- Partner A monthly income: 5000
- Partner B monthly income: 3000
- Partner A protected amount: 1000
- Partner B protected amount: 800
6. Percentage and unit conversions
- Income weights sum to 100%.
- Capacity weights use income minus protection.
- Every policy’s two contributions reconcile to the same need.
7–9. Live substitution, intermediate results, and final result
10. Reverse or reasonableness check
HOW TO USE
Compare rules before choosing one
- Define one shared need that remains fixed across policies.
- Enter incomes on one consistent cash basis.
- Document why each protected amount is included.
- Compare both contributions and retained income.
- Discuss a policy, then save the exact assumptions and review date.
SUBJECT FUNDAMENTALS
Five elements of a contribution policy
- Allocation base
- Quantity used to calculate shares.
- Equal rule
- Same contribution regardless of income.
- Income weight
- Share of combined entered income.
- Capacity weight
- Share after protected amounts.
- Retained income
- Income left after the policy contribution.
MODEL AND FORMULA
Hold the need constant and change only the rule
Equal: C_i=N/2; Income: C_i=N×I_i/ΣI; Capacity: C_i=N×(I_i-P_i)/Σ(I-P)
Apply the same shared need to three separate weighting systems. Equal ignores income; income-proportional uses full income; capacity-weighted subtracts protected amounts first. Retained income is income minus contribution.
DEEPER DECISION ANALYSIS
Why a neutral formula can produce a nonneutral outcome
Protected categories are choices
Capacity weighting depends on which costs or autonomy amounts are protected.
Unpaid work is absent
Care, household labor, career sacrifice, and risk do not appear unless separately addressed.
WORKED DECISION CASES
Two policy-comparison conversations
Large income difference
Compare the retained-income columns rather than debating only percentages.
Temporary protected expense
Add the documented temporary amount, note its end date, and rerun capacity weighting.
TECHNICAL LANGUAGE
Scenario-policy glossary
- Policy
- Explicit rule for dividing one need.
- Allocation base
- Value from which shares are derived.
- Equal split
- Half of need assigned to each person.
- Income-proportional
- Need weighted by full income.
- Capacity-weighted
- Need weighted after protected amounts.
- Minimum retained
- Smaller of the two post-contribution incomes.
EVIDENCE AND DATA LINEAGE
Record the rule as carefully as the numbers
Keep the shared-need ledger, matching-period income evidence, written protection definitions, effective dates, review trigger, and all three output rows. A later decision should be traceable to the exact policy version used.
LIMITS AND EXCLUSIONS
What three scenarios cannot settle
- The calculator does not declare any policy fair.
- It omits unpaid labor, wealth, debt ownership, taxes, benefits, and legal duties.
- It assumes income and need share one monthly basis.
- Protected amounts are user choices, not independently verified necessities.
- It is not legal, financial, tax, counseling, or safety advice.
RELIABLE SOURCES
Primary and authoritative planning references
FREQUENTLY ASKED QUESTIONS
Questions about contribution policies
Which policy is fairest?
The calculator cannot answer that; it shows the consequences of three definitions.
Why show retained income?
It exposes burden that a contribution percentage alone can hide.
Can protected amounts differ?
Yes, but the reason should be explicit and reviewable.
What if need exceeds capacity?
The capacity scenario is rejected because the protected-income plan cannot fund it.
Does income-proportional include allowances?
No. It uses full entered income.
Can more than two people use this?
This implementation is specifically a two-partner comparison.
IMPORTANT NOTE
Comparison is not adjudication
Use the table to support a voluntary, informed agreement. It cannot resolve coercion, legal obligations, ownership, safety, or the value of unpaid work; seek qualified help where those issues matter.
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