How SplitGenius Calculators Work: Our Methodology
SplitGenius uses weighted scoring algorithms to calculate fair splits based on measurable differences between rooms, contributions, and financial situations. Every calculator runs client-side in your browser — no data is sent to our servers. Below we explain each algorithm with formulas, weights, and data sources so you can verify every result.
Rent Split Calculator Methodology
The Rent Split Calculator supports four distinct methods for dividing rent among roommates. Each method suits a different living arrangement, and you can compare results side-by-side.
1. Equal Split
Total rent is divided evenly by the number of roommates. No room features or income differences are considered. This method works when all bedrooms are identical in size and amenities.
2. Square Footage Method
Each person's share is proportional to their bedroom's square footage relative to the total bedroom area. A roommate occupying 60% of the total bedroom space pays 60% of the rent. This approach is objective and easy to verify with a tape measure.
3. Income-Based Method
Rent is divided proportionally by each person's gross monthly income. If one roommate earns $6,000/month and the other earns $4,000/month, the first pays 60% and the second pays 40%. This ensures no one is disproportionately burdened relative to their earning power.
4. Hybrid Method (Recommended)
The hybrid method produces the fairest results by combining multiple room-value factors into a single weighted score. Each room is scored using the following formula:
Score = (sqft_share × 0.40) + (bathroom_bonus × 0.25) + (closet_bonus × 0.15) + (window_bonus × 0.10) + (balcony_bonus × 0.10)Each factor is scored as follows:
Bathroom bonus (25% weight):
- Private full bathroom: 15% premium
- Private half-bath: 5% premium
- Shared bathroom: 0% premium
Closet scoring (15% weight):
- Walk-in closet: 1.0
- Large closet: 0.7
- Standard closet: 0.4
- No closet: 0
Window scoring (10% weight):
- 3+ windows: 1.0
- 2 windows: 0.7
- 1 window: 0.4
- 0 windows: 0
Balcony bonus (10% weight): A room with private balcony or patio access receives a score of 1.0; rooms without receive 0.
Each room's final rent share is calculated as:
Room Rent = (Room Score / Sum of All Room Scores) × Total RentFairness Score Algorithm
Every split generated by SplitGenius includes a Fairness Score from 0 to 100 measuring how equitable the distribution is. The score is calculated using the maximum deviation between any person's actual share percentage and their mathematically ideal share percentage.
FairnessScore = 100 - (maxDeviation × 200)Where maxDeviation is the largest absolute difference between any person's share percentage and their “ideal” share percentage based on the chosen method.
Score interpretation:
- 90–100: Excellent — the split is nearly perfect
- 75–89: Good — minor imbalances that most roommates would accept
- 50–74: Fair — noticeable gaps worth discussing
- Below 50: Poor — significant overpayment or underpayment detected
Affordability & DTI Calculations
The Affordability Calculator and DTI Calculator use the debt-to-income ratio to determine how much rent you can safely afford.
DTI = (Monthly Debt Obligations + Rent) / Gross Monthly IncomeSafe zone thresholds:
- Housing DTI ≤ 28%: considered safe by most lenders and landlords
- Total DTI ≤ 36%: includes all debt obligations (housing, car, student loans, credit cards)
Affordability ranges:
- Comfortable maximum: Gross Monthly Income × 0.30
- Stretch maximum: Gross Monthly Income × 0.40
These thresholds are based on Federal Housing Administration (FHA) guidelines and the widely adopted 50/30/20 budget rule, which allocates 50% of after-tax income to needs (including housing), 30% to wants, and 20% to savings and debt repayment.
Tip Calculation Methodology
The Tip Split Calculator calculates tips on the pre-tax subtotal, which is the standard practice recommended by etiquette experts. Users enter the pre-tax subtotal, and the tip is calculated on that amount.
Per-Person Tip = (Pre-Tax Subtotal × Tip Percentage) / Number of PeopleStandard tip ranges by service type:
| Service | Standard Range |
|---|---|
| Sit-down restaurant | 15–20% |
| Food delivery | 15–20% or $5 minimum |
| Hair salon / barber | 15–25% |
| Hotel housekeeping | $2–$5 per night |
| Taxi / rideshare | 15–20% |
| Counter service / takeout | 0–15% |
Roommate Betrayal Score
The Roommate Betrayal Calculator measures how much a person is overpaying or underpaying relative to their fair share.
Betrayal Score = ((actualPaid - fairShare) / fairShare) × 100A positive score means the person is overpaying. A negative score means they are underpaying. The fair share baseline is calculated using the hybrid room-value method described above.
Magnitude thresholds:
- <5%: Minor — within normal rounding variance
- 5–15%: Moderate — worth a conversation with your roommate
- 15–30%: Significant — you are meaningfully overpaying or underpaying
- >30%: Severe — a major imbalance that should be corrected immediately
Freeloading Index
The Freeloading Index quantifies how evenly two people share the total burden of running a household by combining financial and non-financial contributions.
Total Contribution Score = (Financial % × 0.60) + (Non-Financial % × 0.40)Financial contributions include rent, utilities, groceries, subscriptions, and other shared expenses.
Non-financial contributions include cooking, cleaning, errands, driving, and organizing. Each hour of non-financial labor is valued at $20/hour, based on Bureau of Labor Statistics household labor valuations.
Freeloading Index = |Person A Contribution% - 50| × 2 (scaled 0–100)Verdict thresholds:
- <15: Equal — both partners contribute roughly the same
- 15–29: Slight imbalance — one person does a bit more
- 30–49: Lopsided — there is a clear imbalance worth addressing
- 50–74: Carrying — one person is doing the heavy lifting
- 75+: Freeloader — one person is contributing almost nothing
Data Sources & Standards
Our calculators are grounded in established financial guidelines and publicly available data. The following sources inform our formulas, thresholds, and default values:
- Bureau of Labor Statistics (BLS): Household labor valuations used to price non-financial contributions in the Freeloading Index and Chore Split Calculator
- Federal Housing Administration (FHA): DTI guidelines (28% housing, 36% total) used in the Affordability Calculator and DTI Calculator
- American Institute of CPAs (AICPA): The 50/30/20 budgeting framework used as a baseline for affordability thresholds and the Renter Budget Calculator
- Emily Post Institute & industry surveys: Standard tipping percentages by service type used in the Tip Split Calculator
- HUD Fair Market Rent data: City-level rent benchmarks used in our rent data pages for local affordability context
Transparency Commitment
SplitGenius is built on the principle that financial tools should be transparent, verifiable, and private by default. Here is what that means in practice:
- All calculations run client-side: Every formula executes in your browser using JavaScript. You can verify this by opening your browser's DevTools and inspecting network requests — no data leaves your device.
- No user data collected or stored: We do not have accounts, databases, or server-side storage for calculator inputs. There is nothing to breach because we hold nothing.
- Results encoded in URL parameters: When you share a result, the data is embedded directly in the URL. No database lookup is required, and the link works indefinitely.
- Open methodology: This page documents every formula, weight, and threshold used across all SplitGenius calculators. Nothing is hidden behind proprietary algorithms.
- Last updated: February 2026