You open a retirement calculator. It says you need $1.4 million.
You have $31,000 saved.
That gap feels impossible. Most retirement guides don't help. They either say "just save more" or give you 20 years of theory. Neither one gets you to the actual number you need.
Here's the truth: the math behind retirement is simpler than you think. Two rules explain almost everything. And once you know them, you can calculate your exact number in under five minutes.
Key Takeaways
- The 25x rule: multiply your expected annual retirement expenses by 25 β that's your target portfolio size.
- The 4% rule: withdraw 4% of your portfolio each year, and it should last 30+ years without running out.
- $1 million generates $40,000/year at 4% withdrawal β right for some, too little for others.
- Starting at 25 vs. 35 means you need almost twice the monthly contribution to reach the same target.
- 15% of gross income saved from your 20s onward typically produces a comfortable retirement at 65.
What's your real number?
Find out in seconds. Free. No email.
Calculate My Retirement Number β FreeNo account required
The Two Rules That Drive Every Retirement Calculation
Two rules power virtually every retirement calculator. Once you understand them, the math becomes straightforward.
The 4% Rule
The 4% Rule
This rule is based on 50 years of market data. In year one, you withdraw 4% of your portfolio. Each year after, you adjust for inflation. Your savings should last 30 years or more. For example: a $1,000,000 portfolio at 4% withdrawal produces $40,000/year in retirement income.
William Bengen studied 50 years of market data. He found that a 4% yearly rate held up through every 30-year window on record. That includes the Great Depression and the high inflation of the 1970s.
It's not a guarantee. It's a planning baseline.
β Keep in mind
The 4% rule is calibrated for a 30-year retirement window. If you plan to retire before 65 β at 50 or 55 β consider a more conservative 3β3.5% withdrawal rate, which means saving 29β33x your annual expenses instead of 25x.
The 25x Rule
The 25x Rule
If you can safely withdraw only 4% per year, you need a portfolio worth 25 times your annual expenses. For example: $60,000/year in expenses Γ 25 = a $1,500,000 retirement target.
Retirement Number = Annual Expenses Γ 25
Example: You spend $60,000/year in retirement. Retirement Number = $60,000 Γ 25 = $1,500,000
At 4% withdrawal: $1,500,000 Γ 4% = $60,000/year β
The $1 million figure you keep hearing assumes $40,000/year in expenses. That's the right number for some people β and completely wrong for others.
Your number depends on your lifestyle, not on a generic benchmark.
Step 1: Calculate Your Annual Retirement Expenses
Before running any formula, you need one honest estimate: what will you spend per year in retirement?
Most people underestimate this. Here's a simple framework:
| Expense Category | Retirement Adjustment |
|---|---|
| Housing (rent/mortgage) | Likely lower if paid off |
| Food & groceries | About the same |
| Healthcare | Higher β budget +$6,000/year |
| Transportation | Lower β no commute |
| Travel & leisure | Higher in early retirement |
| Taxes | Lower, but not zero |
A common estimate: retirement spending is roughly 70β80% of pre-retirement income for most people. Healthcare is the wild card. Costs often rise with age. If you retire before 65, they're highest in the years before Medicare starts.
β² Check before you proceed
If you retire before 65, you'll face a coverage gap before Medicare eligibility. Private insurance premiums during those years often run $12,000β$20,000 per year for a couple β budget this separately. It's the most common retirement planning blind spot.
Step 2: Apply the 25x Formula
Once you have your annual expense estimate, the math is straightforward.
Retirement Number = Annual Expenses Γ 25
Three scenarios:
Lean retirement ($45,000/yr expenses) $45,000 Γ 25 = $1,125,000
Moderate retirement ($70,000/yr expenses) $70,000 Γ 25 = $1,750,000
Comfortable retirement ($100,000/yr expenses) $100,000 Γ 25 = $2,500,000
These numbers look large. But they're not what you need to save from scratch β they're what your portfolio needs to be worth on the day you retire. Compound growth does most of the work.
What's your real number?
Find out in seconds. Free. No email.
Run My Retirement Scenarios β FreeNo account required
Step 3: Calculate How Much to Save Each Month
This is the part most calculators skip. How much do you need to set aside each month to actually reach your number?
The formula shows how your monthly deposits grow over time.
FV = PMT Γ [((1 + r)βΏ β 1) Γ· r]
Where: FV = future portfolio value (your retirement number) PMT = monthly contribution r = monthly return rate (annual return Γ· 12) n = number of months until retirement
Solving for PMT (monthly contribution): PMT = FV Γ r Γ· [((1 + r)βΏ β 1)]
Let's put real numbers to it. You're 30 years old. You want $1,500,000 by age 65. You assume 7% average annual return.
FV = $1,500,000 r = 7% Γ· 12 = 0.5833% per month = 0.005833 n = 35 years Γ 12 = 420 months
PMT = 1,500,000 Γ 0.005833 Γ· [((1.005833)β΄Β²β° β 1)]
(1.005833)β΄Β²β° β 11.39 PMT = 8,750 Γ· (11.39 β 1) PMT = 8,750 Γ· 10.39
β PMT β $842/month
$842/month for 35 years, at 7% annual return, reaches $1,500,000.
Total contributed: $842 Γ 420 = $353,640. Growth from compounding: $1,500,000 β $353,640 = $1,146,360 from investment returns alone. That's the power of starting early.
Why Starting Early Beats Contributing More
Here's the counterintuitive part. Same $1,500,000 target β just starting at different ages.
| Starting Age | Monthly Needed | Total Contributed | Growth From Returns |
|---|---|---|---|
| 25 | $611/mo | $293,280 | $1,206,720 |
| 30 | $842/mo | $353,640 | $1,146,360 |
| 35 | $1,188/mo | $428,880 | $1,071,120 |
| 40 | $1,733/mo | $519,900 | $980,100 |
| 45 | $2,633/mo | $631,920 | $868,080 |
Waiting 10 years β from 25 to 35 β means you need to contribute almost twice as much per month to reach the same goal.
Here's the kicker. The person who starts at 25 puts in $135,000 less than the one who starts at 35. They still reach the same goal. Time is the variable you control most β and the one you can never get back.
Β» MORE: See how an employer 401(k) match cuts your monthly contribution β 401(k) Calculator
The Inflation Problem Nobody Talks About
The 25x rule tells you how much you need in today's dollars. But retirement is 20β35 years away. Inflation erodes purchasing power every single year.
Inflation Adjustment Formula: Future Value Needed = Today's Value Γ (1 + inflation rate)βΏ
Example: Today's retirement number: $1,500,000 Inflation rate: 3% per year Years until retirement: 30
Inflation-adjusted target = $1,500,000 Γ (1.03)Β³β° (1.03)Β³β° β 2.43
β Inflation-adjusted target β $3,645,000
That looks alarming. But your investments also grow. Say your portfolio earns 7% and inflation runs at 3%. Your real gain is about 4% per year. The 4% rule is built to handle inflation. That's why the 25x formula still works. Just use your current expenses as the starting point.
The key: don't inflate your expense estimate. Use what you spend today, and let the 4% rule handle the rest.
The 15% Rule
If the formulas feel like too much right now, here's the shortcut most financial planners agree on.
The 15% Rule: Save 15% of your gross income starting in your 20s. Includes employer 401(k) match.
Example: Gross income: $75,000/year 15% = $11,250/year = $937.50/month
At 7% average return over 35 years: $937.50/month β approximately $1,620,000
This rule won't fit everyone. If you started late, earn less, or plan to spend more in retirement, you'll need to save more. But as a floor β it's a solid place to start.
β Important
Starting late changes the math significantly. A 45-year-old targeting $1,500,000 by 65 needs roughly $2,633/month β about 35β40% of a $75,000 salary. If that's not feasible, the levers are: push retirement back a few years, reduce expected expenses, or plan for part-time income in early retirement.
4 Actions to Take This Week
1. Estimate your annual retirement expenses
Start with what you spend each month now. Then adjust for what will change: no mortgage, higher medical costs, and more travel early on. Write down one number. That's your baseline.
2. Calculate your retirement target
Multiply your annual expense estimate by 25. That's your number. It might surprise you β in either direction. Most people find it's more achievable than they feared once they see the compound growth math.
3. Check your current savings rate
What percentage of your gross income goes to retirement accounts right now? If it's below 10%, you have a gap to close. Even moving from 6% to 10% makes a meaningful difference over decades.
4. Run the retirement calculator
Plug in your age, current savings, monthly contribution, and expected return. See your projected balance at 65. Then change one thing at a time. A small boost to your monthly savings today can make a big difference 30 years from now.
What Your Retirement Number Actually Means
Your retirement number isn't a verdict on where you stand today. It's a planning target β one that compound growth works toward the moment you start contributing.
The math doesn't care whether you start at 25 or 45. It cares about how much time it has to work. A 35-year-old contributing $842/month reaches $1.5 million by 65. A 45-year-old contributing $2,633/month reaches the same number. Different paths β same destination.
When you know your number, every money choice looks different. Use our retirement calculator to find your number. Then check our 401(k) calculator to see how your employer match speeds things up.
The Bottom Line
Multiply your expected annual retirement expenses by 25 β that's your number. For most people spending $60,000β$70,000 a year in retirement, the target lands between $1.5 million and $1.75 million. A 30-year-old contributing $842/month at 7% annual return reaches $1.5 million by 65 β and compound growth does most of the heavy lifting. Start with the retirement calculator to find your exact target, then lock in a monthly contribution you can sustain today.
Common Questions
Sources & Methodology
The 4% rule is based on Bengen (1994), "Determining Withdrawal Rates Using Historical Data," Journal of Financial Planning. Future value calculations use the standard FV annuity formula: FV = PMT Γ [((1 + r)βΏ β 1) Γ· r]. Return assumptions of 7% reflect historical long-term blended portfolio averages before inflation.
Sources: Employee Benefit Security Administration β DOL, Social Security Administration β Retirement Benefits, Federal Reserve Bank of St. Louis (FRED).
Published: May 2026 | Last updated: May 2026 | By: FiscalCalc Editorial Team
Disclaimer: Results are for educational and informational purposes only. FiscalCalc is not a licensed financial advisor, mortgage broker, or tax professional. Consult a qualified professional before making major financial decisions.