How Long Will My Money Last? Personal Runway Calculator Guide

"How long will my money last?" is one of the most common personal finance questions on the internet. The answer is the same math startups use to calculate runway. Three numbers, one division.

The personal runway formula

Same formula as startup runway:

Personal runway (months) = Savings ÷ Monthly net burn

Where monthly net burn equals your monthly expenses minus your monthly income.

A worked example

You are considering taking a 6-month sabbatical to travel. You want to know if your savings will hold.

• Savings: $42,000
• Monthly expenses while traveling: $3,800
• Side income (freelance gigs): $1,200/month
• Net monthly burn: $3,800 − $1,200 = $2,600
• Personal runway: $42,000 ÷ $2,600 = 16.2 months

You have 16 months of runway. A 6-month sabbatical fits comfortably with a 10-month buffer. Now you can leave with confidence.

When to use personal runway thinking

• Before quitting a job to start a business or take time off
• During a job loss to know how long the emergency fund will hold
• Planning a sabbatical or extended travel
• Considering a career switch that may involve a salary cut
• Going freelance with unpredictable income
• Caregiving leave when you need to step away from work
• Early retirement planning (this is the basis of FIRE math)

The four runway thresholds

Runway	Status	What it means
24+ months	Comfortable	Plenty of room to make decisions slowly
12-24 months	Healthy	Standard emergency fund range
6-12 months	Watch zone	Time to actively pursue income
Under 6 months	Pressure	Hard choices: side gig, job, cut expenses

What to include in monthly expenses

Be honest. Include everything that hits your account in a typical month:

• Rent or mortgage
• Utilities (electric, gas, water, internet)
• Phone
• Groceries
• Eating out (yes, this counts)
• Transportation (gas, car payment, insurance, transit)
• Health insurance and medical
• Subscriptions (streaming, gym, software)
• Personal care
• Entertainment
• Debt minimums (credit cards, loans)
• Pet care if applicable
• Childcare if applicable
• Insurance (renters, auto, life)
• Personal taxes if self-employed

Most people underestimate their monthly burn by 20-30% because they forget irregular expenses (car repairs, gifts, doctor visits, annual subscriptions). Build a buffer of 10-15% into your "monthly expenses" number to account for these.

Sources of monthly income (revenue side)

• Salary or wages
• Freelance / contract income
• Dividends and interest
• Rental income (after expenses)
• Side hustle income
• Spouse income (if shared finances)
• Pension or Social Security (if applicable)

Use realistic averages. If freelance income varies between $0 and $4,000 a month, use a conservative number like $1,500, not the high end.

The "savings runway" mindset shift

Most people think of savings as a bucket — full or empty. Runway thinking turns it into a clock — months remaining. The shift is powerful because it makes financial decisions concrete.

"Should I buy this $2,400 couch?" is hard to answer. "Should I trade one month of runway for this couch?" is easier. (Maybe yes, maybe no — but the trade is now visible.)

Use the same calculator

The burn rate calculator works for personal finance with no modifications. Bank balance is your savings. Monthly expenses are your full monthly cost of living. Monthly revenue is any income you receive. The calculator shows your runway and the exact date your money runs out.

Run the math once. Then update it on the first of every month. You will know exactly where you stand, every month, in 30 seconds. That alone removes most financial anxiety.