joellewis/emergency-fund

Emergency Fund Planning

Core Concepts

Rule of Thumb

• Employed with stable income: 3-6 months of essential expenses
• Dual-income household (both stable): 3 months may suffice (lower probability of simultaneous job loss)
• Single income, variable income, or self-employed: 6-12 months of essential expenses
• High job-search risk (niche industry, senior executive, specialized role): 6-12 months
• These are guidelines — individual assessment is essential

Essential Expenses

The emergency fund should cover non-discretionary spending only:

• Housing: Mortgage/rent, property tax, insurance, HOA
• Food: Groceries (not dining out)
• Insurance: Health, auto, life (premiums that cannot be paused)
• Utilities: Electric, gas, water, internet, phone
• Transportation: Car payment, gas, basic maintenance, public transit
• Minimum debt payments: Credit cards, student loans, other obligations
• Healthcare: Regular medications, co-pays
• Exclude: Dining out, entertainment, travel, shopping, subscriptions that can be cancelled

Expense-Based Sizing

Monthly essential expenses multiplied by the desired months of coverage:

• Emergency fund = monthly essential expenses × months of coverage
• Example: $4,500/month essentials × 6 months = $27,000
• More precise than income-based because it reflects actual spending needs during a crisis

Income Replacement Approach

After-tax monthly income multiplied by months of coverage:

• Emergency fund = after-tax monthly income × months of coverage
• Simpler to calculate but may overstate need (assumes maintaining full spending during emergency)
• Useful as an upper bound or for high earners whose expenses scale with income

Variable Income Adjustment

For commission-based, freelance, seasonal, or gig workers:

• Calculate average monthly income over 12-24 months
• Set base budget at the lowest 3-month average income level
• Buffer = average income - base budget (accumulated during high-earning months)
• Emergency fund should be 6-12 months of essential expenses (longer because income disruption is more likely and less predictable)
• Maintain a separate "income smoothing" buffer beyond the emergency fund

Tiered Emergency Fund

Structure the fund across tiers for optimal balance of access and yield:

• Tier 1 — Immediate access (1 month): Checking or savings account at primary bank. Instantly accessible for urgent needs. Low or no yield, but maximum liquidity.
• Tier 2 — Short-term (2-3 months): High-yield savings account (HYSA) or money market fund. Available in 1-2 business days. Earns competitive short-term rates.
• Tier 3 — Extended (3-6 months): Short-term Treasury bills, I-bonds (after 1-year lock-up), short-term bond fund, or CD ladder. May take a few days to a few weeks to access. Higher yield compensates for slightly lower liquidity.

Vehicle Selection

| Vehicle | Yield | Liquidity | FDIC/SIPC | Best For | |---------|-------|-----------|-----------|----------| | Checking account | Very low | Instant | FDIC | Tier 1 (1 month) | | HYSA | Moderate | 1-2 days | FDIC | Tier 2 (core fund) | | Money market fund | Moderate | 1-2 days | SIPC | Tier 2 (core fund) | | T-bills (4-week) | Moderate-high | At maturity | Full faith & credit | Tier 2/3 (ladder) | | CD (3-12 month) | Moderate-high | At maturity (penalty) | FDIC | Tier 3 (ladder) | | I-bonds | Inflation-linked | After 12 months | Full faith & credit | Tier 3 (long-term) | | Short-term bond fund | Variable | 1-3 days | SIPC | Tier 3 (flexible) |

Opportunity Cost

Holding cash has a real cost — the difference between what the cash earns and what it could earn if invested:

• Cash drag: Emergency fund earning 4% HYSA vs 8-10% equity expected return = 4-6% annual opportunity cost
• On a $30K emergency fund: $1,200-$1,800/year in foregone returns
• Mitigant: The purpose of the fund is insurance, not investment return. The "premium" is the opportunity cost.
• Over-funded risk: Holding 12+ months when 3-6 months suffices wastes significant capital
• Under-funded risk: Having to use credit cards at 20%+ APR or sell investments at a loss during an emergency

When to Tap the Emergency Fund

Appropriate uses:

• Job loss or significant income reduction
• Medical emergency or unexpected healthcare costs
• Essential home repair (roof leak, HVAC failure, plumbing emergency)
• Essential car repair (needed for commuting to work)
• Unexpected essential travel (family emergency)

NOT appropriate uses:

• Vacations or planned travel
• Planned purchases (holiday gifts, electronics)
• Investment opportunities ("buy the dip")
• Non-essential home improvements
• Expenses that should have been budgeted (annual insurance, property tax)

Replenishment Plan

After using the emergency fund:

• Prioritize rebuilding before resuming discretionary spending or non-essential savings goals
• Set a monthly replenishment target (e.g., rebuild within 6-12 months)
• Temporarily reduce or pause contributions to other goals if needed
• Redirect windfalls (tax refund, bonus) to accelerate replenishment

Key Formulas

| Formula | Expression | Use Case | |---------|-----------|----------| | Expense-based fund | Monthly essentials × months of coverage | Core sizing calculation | | Income-based fund | After-tax monthly income × months of coverage | Upper bound estimate | | Opportunity cost | Fund balance × (investment return - cash return) | Cost of holding cash | | Replenishment timeline | Fund shortfall / monthly replenishment amount | Months to rebuild | | Variable income buffer | Avg monthly income - base budget | Surplus for smoothing |

Worked Examples

Example 1: Emergency fund sizing for a dual-income household

Given: Married couple, both employed in stable jobs. Monthly essential expenses: $4,500 (housing $1,800, food $600, insurance $400, utilities $300, transportation $500, debt minimums $400, healthcare $200, other essentials $300). Calculate: Recommended emergency fund size. Solution:

1. Dual income, stable employment: 3 months is the baseline; 4 months provides a comfortable margin.
2. Emergency fund = $4,500 × 3 = $13,500 (minimum) to $4,500 × 4 = $18,000 (recommended).
3. Considerations: If either spouse works in a cyclical industry or has less job security, increase to 6 months ($27,000).
4. If one spouse could cover essentials alone: May reduce to 3 months since the risk of zero income is lower.
5. Recommendation: $13,500-$18,000 for this stable dual-income household.

Example 2: Tiered fund allocation

Given: Target emergency fund of $27,000 (6 months × $4,500/month) for a single-income household. Calculate: Optimal tiered allocation. Solution:

1. Tier 1 — Checking account: $4,500 (1 month). Immediate access for sudden expenses (car repair, medical co-pay). Earning ~0.01% but provides instant liquidity.
2. Tier 2 — High-yield savings account: $13,500 (3 months). Core emergency reserves. Earning ~4.5% APY (e.g., ~4-5% as of 2025 — check current HYSA rates). Available in 1-2 business days via transfer.
3. Tier 3 — T-bill ladder: $9,000 (2 months). Three $3,000 T-bills maturing at 4-week, 8-week, and 13-week intervals. Earning ~4.8% (e.g., ~4-5% as of 2025 — check current T-bill rates). At least one tranche matures every ~4 weeks.
4. Blended yield: (4,500 × 0.01% + 13,500 × 4.5% + 9,000 × 4.8%) / 27,000 ≈ 3.85% weighted average.
5. vs all checking (0.01%): Earning ~$1,040/year more with the tiered approach — effectively free money for modest complexity.

Common Pitfalls

• Too little: financial stress during emergencies, forced to use high-interest debt (credit cards at 20%+), potential to sell investments at a loss
• Too much: significant opportunity cost from excess cash eroded by inflation; common among risk-averse savers
• Not adjusting for life changes — new baby (higher expenses), job change (less stability), mortgage (larger fixed obligation), spouse stops working
• Keeping the emergency fund in investments that can lose value — stocks, long-term bonds, or crypto are not appropriate vehicles
• Using the emergency fund for non-emergencies — erodes the safety net and creates a cycle of depletion
• Not having a replenishment plan — spending the fund without a strategy to rebuild leaves ongoing vulnerability
• Ignoring inflation: a $20K fund in 2020 has less purchasing power in 2030; periodically reassess the target
• Treating the emergency fund as an investment account rather than an insurance policy

Cross-References

• liquidity-management: emergency fund is the foundation of the personal liquidity tier structure
• savings-goals: emergency fund is typically the highest priority savings goal
• debt-management: adequate emergency fund prevents taking on new high-interest debt during crises
• lending: emergency reserves are a factor in mortgage qualification
• investment-policy: emergency fund size feeds the liquidity constraint in an IPS
• financial-planning-workflow (advisory-practice plugin): emergency fund adequacy is assessed early in the comprehensive financial planning process

Running the Script

uv run scripts/emergency_fund.py            # run the demo (uses PEP 723 inline deps)
uv run scripts/emergency_fund.py --verify   # check demo outputs against the worked examples (exit 1 on mismatch)
python3 scripts/emergency_fund.py            # alternative (requires: pip install numpy)

The demo prints the calculations covered above; its values match the worked examples in this skill. Run --help for a list of the classes and functions. For programmatic use, import the module rather than running it — the demo only executes under python emergency_fund.py.