The Foundations
Runway
Runway

Three Questions.
One Calculator.

Every retirement plan starts with one of three questions. Set your situation once, then explore each scenario below.

Your Situation
Scenario Targets
Desired Retirement Age 60
Target Monthly Spend $8K
Enter your pre-tax target.
Personal
Current Age 35
Plan to Age 99
Current Retirement Savings
Annual Contributions
Contributors
Single
Couple
Account Type
401k
IRA
Both
Annual Amount
$23,500 100% of max
$0 IRS max: $23,500
Include Social Security — Primary
Monthly Benefit (at Full Retirement Age)
Election Age × 1.24 · maximum benefit
Early
Age 62
Full
Age 67
Delayed
Age 70
Adjust assumptions to stress-test your plan
Fat-tailed returns (t-dist, df=4) · Sequence-of-returns haircut applied years 0–7
Expected Return 7.0%
Conservative
5%Lost Decade of 2000s
Default
7%30yr avg 1990–2020
Aggressive
9%Bull Run of 2010s
Inflation Rate 3.0%
Elevated
4%
Default
3%
Optimistic
2%
Withdrawal Rate 4.0%
Cautious
3.5%
Default
4%
Aggressive
4.5%
01
Income Mode
How much will I have
to live on?
I have what I have. Tell me what it buys me.
↓
↳ What this answers

Given your savings and contributions, how much can you sustainably spend each month in retirement?

Uses: current savings · contributions · desired retirement age

◎
Run calculation to see results
Your Target Spend
—
per month
Cautious · 90% success rate
—
—
Balanced · 85% success rate
—
—
Flexible · 75% success rate
—
—
COLOR KEY: ■ On target ■ Within 10% ■ >10% shortfall
Success rate at target · —yr retirement
—
Nest Egg at Retirement
—
Years in Retirement
—
SS Income / mo
—
↳ Key Insight
—
↳ Understanding the success rates
Each success rate is the result of a Monte Carlo simulation — 2,000 independent retirement scenarios, each with a different sequence of randomized market returns drawn from historical distributions. The percentage shown is how many of those simulations ended with money still remaining.

90% Cautious — 9 in 10 scenarios succeed. Maximum buffer for bad sequence-of-returns.

85% Balanced — 17 in 20 succeed. The conventional planning standard. Accepts moderate tail risk.

75% Flexible — 3 in 4 succeed. Assumes you can trim spending if markets underperform.
02
Goal Mode
How much do I
need to save?
I know the life I want. Tell me the price tag.
↓
↳ What this answers

Given a target monthly spend, what nest egg do you need at your chosen MC confidence level — and are you on track?

Uses: target monthly spend · desired retirement age · MC threshold

◎
Run calculation to see results
Required Nest Egg at Retirement
Projected: —
Cautious · 90% success rate
—
—
—
Balanced · 85% success rate
—
—
—
Flexible · 75% success rate
—
—
—
↳ Key Insight
—
03
Progress Mode
How long do I need
to keep working?
I'm on a path. Tell me how far I am.
↓
↳ What this answers

Given a target monthly spend, at what age do your savings cross the Runway threshold?

Uses: target monthly spend · current savings · contributions

◎
Run calculation to see results
MC · each row is an independent lever
75%
85%
90%
Retire when? · hold spend at $—/mo
—
—
Spend how much? · retire at —
—
—
Money lasts to? · retire at —, spend $—/mo
—
—
↳ Key Insight
—
For educational purposes only. Not financial advice. Simulations use historical return assumptions and are illustrative only. Consult a qualified financial planner (CFA/CFP) for personalized guidance.
Adjust Assumptions
Expected Return 7.0%
Conservative
5%
Default
7%
Aggressive
9%
Inflation Rate 3.0%
Elevated
4%
Default
3%
Optimistic
2%
Withdrawal Rate 4.0%
Cautious
3.5%
Default
4%
Aggressive
4.5%
Runway
Step 1 of 5
Let's set up your plan

Are you planning alone or with a partner?

This determines which income sources and timelines we model.

Your savings

How much do you have saved for retirement?

Include 401(k), IRA, brokerage — anything you'd draw on. Round numbers are fine.

Current retirement savings
≈ $150K
Annual contributions$23,500
2025 401(k) limit: $23,500. Age 50+ catchup adds $7,500.
Your timeline

When do you want to stop working?

Rough targets are fine. Everything is adjustable after.

Your current age35
Your target retirement age60
25 years away — money doubles roughly 2.5× at 7%.
Plan to age99
Planning conservatively on lifespan is the only honest assumption.
Social Security

Do you have your SSA estimate?

The single biggest income source most people underestimate.

Your monthly benefit at FRA$3,000
ℹ
Find this at ssa.gov/myaccount → Your Statements → Estimated Benefits. Use the Full Retirement Age column (age 67 for most). The calculator applies the 24% delay credit for claiming at 70.
Last one

What's your target monthly spend in retirement?

In today's dollars. Every $1M saved supports roughly $3,300/mo for 30 years.

Monthly spend target$8,000
Here's what we'll use