How to Calculate Your Financial Runway

What "Financial Runway" Means

Financial runway is the number of months your liquid savings can sustain your life if your income stopped today. It's the most direct measure of financial resilience — not net worth, not total savings, but specifically how long you could survive a crisis without borrowing.

The calculation is straightforward in principle but depends heavily on which costs you include and whether you model emergency cost reductions.

The Basic Calculation

"Liquid savings" means cash or near-cash you can access within a few days — current accounts, instant-access savings, cash ISAs. It excludes pension pots (penalties and tax charges make these expensive to access early), property equity (illiquid), investments in volatile assets, or Premium Bonds with slow redemption.

The "3–6 Month" Rule — Where It Comes From

The conventional advice to hold 3–6 months of expenses as an emergency fund is a heuristic derived from average unemployment durations in developed economies. In the UK, the median time to re-employment after job loss is approximately 3–4 months. Six months covers the 75th–80th percentile of unemployment spells.

The right number for any individual depends on income stability (employed vs self-employed), number of dependants, sector cyclicality, ability to cut costs quickly, and access to credit as a temporary backstop.

What-If: Cost-of-Living Shock + Income Loss

Financial crises don't always mean zero income — they often mean a combination of income reduction and cost increases simultaneously. Redundancy may come with reduced income (statutory redundancy pay, then benefits), while inflation or healthcare costs increase expenses.

What-If: How Expense Cuts Extend Runway

Emergency expense cuts (cancelling subscriptions, reducing dining, deferring non-essential purchases) typically reduce monthly outgoings by 20–35% for most households. The runway extension is proportionally significant:

A 35% expense reduction extends the runway by 55% — the relationship is non-linear because the same fixed savings pool is divided by a smaller burn rate. This is why financial advisers emphasise having an identified list of cuttable expenses before a crisis, not during one.

What Counts as Liquid

• Include: Current accounts, instant-access savings, easy-access cash ISAs, Premium Bonds (allow 3–5 days redemption)
• Exclude with caution: Notice accounts (30–180 day notice period), fixed-term bonds (penalties), S&S ISAs (liquid but volatile — selling in a downturn crystallises losses)
• Exclude entirely: Pension pots (55+ access; 25% tax-free, remainder taxed as income), property equity (months to access), business assets

Beyond the Number: What the Runway Tells You

Runway is a risk metric, not a target. A 6-month runway doesn't mean the goal is achieved — it means there's 6 months to find a solution. The relevant questions: how long would re-employment realistically take in your sector, at your seniority level, in current market conditions? What are the minimum expenses that cannot be cut (rent, utilities, food, debt service)? Is there a credit facility (0% overdraft, credit card) that buys additional time without catastrophic cost?

The Plain Figures Crisis Simulator models the burndown graphically — showing exactly when savings hit zero under different expense-cut and income-replacement scenarios. The goal is clarity before the situation arises.

Frequently Asked Questions

What counts as a financial crisis for this calculator?

Any scenario where monthly expenses exceed monthly income — job loss, significant income reduction, sudden large expense, or a combination. The calculator models the depletion of liquid savings under a given burn rate. The trigger event doesn't need to be catastrophic; even a 30% income cut against fixed costs can produce a runway problem within 12 months.

Should I include my stocks and shares ISA in liquid savings?

With caution. Stocks and shares ISAs are technically accessible but carry sequencing risk — selling during a market downturn crystallises losses permanently. A conservative approach excludes them from liquid savings calculations. If included, apply a stress discount of 20–40% to reflect potential drawdown at time of crisis.

How much emergency fund do I actually need?

The conventional 3–6 months is a population average heuristic. Self-employed and contract workers should target 6–12 months. The right number depends on your minimum non-negotiable monthly expenses (rent/mortgage, utilities, food, debt service), how quickly your income could realistically recover, and whether you have any flexible credit available as a buffer.

Does the 3–6 month rule refer to income or expenses?

Expenses — specifically your minimum essential monthly outgoings, not your gross income. The purpose is to cover what you must pay during a crisis, not to replace your full lifestyle. Many people with modest savings have adequate runway because their minimum essential expenses are significantly below their income.