Retirement Calculator V1

Tool Overview

This tool stress-tests your retirement plan using a Monte Carlo simulation. You enter your current age, retirement age, current savings, how much you save each month, how much you plan to spend each month in retirement, your stock versus bond allocation, and how long you want your money to last. The tool runs 500 random market scenarios from now until that end age. It shows you the chance that your money will not run out. It also shows a chart of your portfolio balance over time in a likely case, a best case, and a worst case. If your chance of success is low, a safety finder suggests changes you can apply with one click: save more, spend less in retirement, delay retirement, or adjust stock allocation.

Many people wonder if they will have enough to retire. A single average return hides the risk of bad years early in retirement. That is called sequence of returns risk. This tool runs many random paths. You see how often your plan would have worked. You see when money might run out in the worst cases. You get concrete suggestions to improve your odds. So you get a clearer picture of risk and what to change.

The tool is for anyone who is saving for retirement and wants to test their plan. Employees, savers, and people near retirement use it. You do not need finance expertise. You fill in numbers from your accounts and budget. A first-time user can run a simulation in a few steps. An optional AI advisor can give personalized text advice based on your inputs and results.

Background and Concept

Retirement planning means saving now and spending later. You save each year and invest. After you retire you stop saving and start spending from the portfolio. If the market does well, your money can last. If the market does badly early in retirement, you may run out sooner. The order of good and bad years matters. That is sequence of returns risk. A Monte Carlo simulation does not use one average return. It draws a random return each year from a distribution. It runs hundreds of times. Each run is one possible future. At the end you see how many runs left you with money and how many ran out.

Success in this tool means your portfolio balance stayed above zero until the end age you set. The tool simulates from your current age to that age. Before retirement it adds your monthly contribution each year. After retirement it subtracts your monthly spending each year. Market returns are random. So each run can end with a positive balance or zero. The success probability is the share of runs that did not run out.

People struggle because they use one average return and ignore bad sequences. This tool runs 500 paths with random returns and shows you the spread. A safety finder then suggests changes to improve your odds. So you see the risk and get actionable steps.

Key Features

• Your parameters. You enter current age (18 to 80), retirement age (at least current age plus one, up to 90), current savings in dollars, monthly contribution in dollars, monthly spend in retirement in today's dollars, stock allocation as a percent (0 to 100), and longevity test age (80 to 110). So the tool knows your timeline, savings rate, spending goal, and how long you want money to last.
• Monte Carlo simulation. The tool runs 500 paths. Each year it applies a random portfolio return based on your stock and bond allocation, then adds contributions before retirement or subtracts spending after retirement. Balance is never set below zero. So you get a range of outcomes, not one line.
• Success probability. The tool counts how many of the 500 runs had a positive balance at the end age. That count as a percent is your chance of funding retirement. So you see how often your plan would have worked.
• Projected portfolio balance chart. For each year the tool shows the 10th percentile (pessimistic), 50th (likely), and 90th (optimistic) balance across the 500 runs. A chart plots these three lines by age. A dashed line marks retirement age. So you see the band of possible outcomes and when you stop saving and start spending.
• Market Sensitivity tab. The chart lives in this tab. A note states that the simulation uses 500 iterations and that pessimistic is the bottom 10% of outcomes (timing risk). So you know what the lines mean.
• Safety Margin Finder tab. If your success probability is below 90%, the tool lists risk adjustments. Each item has a suggestion and an impact line. Some have an Apply this suggestion button that sets the suggested value into your parameters. Suggestions can include: increase equity allocation if you are very conservative and have time; reduce equity if you are very aggressive and close to retirement; increase monthly savings to close a shortfall; delay retirement by a year or two; reduce retirement spending by 10%; or a longevity warning if in bad scenarios money runs out before your end age. So you get concrete steps to improve your plan.
• Safe zone message. If your success probability is 90% or higher, the safety tab shows a message that you are in the safe zone and might consider spending more or retiring earlier. So you know when the plan is strong.
• Optional AI advisor. A Personalized AI Advisor section has an Analyze My Plan button. It sends your inputs and results to an AI service and shows paragraph-style advice. This is optional. If the service fails, you see a message to try again later. You can clear the advice and run a new analysis. So you can get tailored text without changing the math.

Common Use Cases

Checking if you are on track. You enter your age, retirement age, savings, monthly contribution, and expected retirement spending. You set stock allocation and how long you want money to last. You read the success probability and the chart. So you see whether your plan is strong or risky.

Testing more savings. You wonder what happens if you save more. You raise the monthly contribution slider. The simulation reruns. You see a higher success probability and often higher balances in the chart. You can apply a safety suggestion to increase savings and see the new result. So you decide how much to save.

Testing later retirement. You consider working longer. You increase retirement age. The tool runs again. You see more years of contributions and fewer years of spending. Success probability often goes up. You can apply a suggestion to delay retirement and compare. So you weigh working longer.

Testing longevity. You want to see if money lasts if you live to 95 or 100. You set the longevity test age to that value. You run the simulation. You see success probability and the chart to that age. If the safety finder shows a longevity risk message, you know funds may run out early in bad scenarios. So you plan for a long life.

Getting AI advice. After viewing your results you click Analyze My Plan. The AI returns paragraphs of advice. You use them as ideas, not as guaranteed recommendations. So you get next steps to improve your plan.

How to Use This Tool

1. Enter your parameters. In the Your Parameters section set current age, retirement age, current savings, monthly contribution, monthly spend in retirement (in today's dollars), stock allocation percent, and longevity test age. Use the sliders or type values. Use numbers from your accounts and budget.
2. Read the results. The right side shows Success Probability (percent chance of funding retirement) and an icon (green for high, yellow for medium, red for low). Below is a note on your portfolio mix and years. If you see an error message, check your inputs.
3. Open the Market Sensitivity tab. You see the chart of projected portfolio balance by age with optimistic, likely, and pessimistic lines and a retirement age line. Use the chart to see when balances grow or fall and how wide the range is.
4. Open the Safety Margin Finder tab. If your probability is below 90%, you see a list of risk adjustments. Each has a suggestion and impact. If a suggestion has an Apply this suggestion link, click it to put the suggested value into your parameters. The simulation will rerun. So you can try suggested changes with one click.
5. If your probability is 90% or higher, the safety tab shows a safe zone message. You might consider spending more or retiring earlier.
6. Optional: get AI advice. In the Personalized AI Advisor section click Analyze My Plan. Wait while it analyzes. You will see paragraph-style advice. If you see an error, try again later. Click Run New Analysis to clear and run again.
7. On small screens use the View Results button to scroll to the results section. Adjust any parameter and watch the probability and chart update after a short delay.

Calculations and Logic

The tool runs 500 paths from your current age to your longevity test age. Each year it computes a portfolio return. The return is a blend of stock and bond assumptions: stock mean return 7% with 15% volatility, bond mean 3% with 5% volatility. Your stock allocation sets the blend. A random return is drawn from a normal distribution with that blend. Balance is multiplied by (1 plus that return). Before retirement the tool adds 12 times your monthly contribution. After retirement it subtracts 12 times your monthly spending. Balance is never set below zero. So each path is one possible future.

After all 500 paths, for each year the tool sorts the 500 balances and takes the 10th, 50th, and 90th percentiles. Those are the pessimistic, likely, and optimistic values for that age. The chart and the median final balance use these. Success probability is the number of paths that ended with a positive balance, divided by 500, as a percent. If some paths ran out, the tool can report an average age at which money ran out.

The safety finder uses your success probability and inputs. If probability is at least 90%, it returns no suggestions. Otherwise it can suggest: increase or decrease equity allocation based on current allocation and years to retirement; increase monthly contribution to close a shortfall (shortfall is based on a 4% rule: required portfolio is 25 times annual retirement spending); delay retirement by one or two years if probability is below 85% and retirement age is under 70; reduce retirement spending by 10% if probability is below 75% and spending is above a threshold; or a longevity risk message if in failed runs money ran out before your longevity age. Some suggestions include a value you can apply so the tool updates your inputs. So you get actionable steps, not just text.

The tool does not include Social Security or pensions. It does not ask for income or tax. It uses fixed market assumptions. So you interpret the probability and suggestions in light of your full picture.

Tips, Limitations, and Best Practices

Use numbers you can verify: savings from statements, contribution and spending from your budget. Set retirement age to when you expect to stop full-time work. Set monthly spend in retirement in today's dollars; the simulation uses that amount each year in retirement. Set longevity test age to how long you want to plan for (for example 95 or 100). Stock allocation affects both return and volatility; higher stock usually means higher expected return but wider outcomes.

Limitations: the simulation uses fixed stock and bond return and volatility assumptions. Real markets differ. Success means balance above zero; it does not model taxes, health costs, or one-time expenses. The safety finder uses a simple 4% rule and shortfall math; it does not replace a full plan. The AI advisor depends on an external service; it can fail or be unavailable. The tool is for planning and education only. It is not investment or tax advice.

For best results, run the simulation with your real numbers first. Use the Safety Margin Finder to see suggested changes and apply them one at a time to see how probability and the chart change. Try a higher longevity age to stress-test a long life. Use the optional AI advice as ideas, then verify any changes with your own situation or a professional if needed.