Coast FIRE Gap Calculator
Measure the difference between your current investments and Coast FIRE target. Set a deadline to estimate the monthly contribution required, or use your current contribution to calculate a projected catch-up date.
Reach Target by Deadline: Choose a target date and calculate the estimated monthly contribution required to reach your Coast FIRE number.
Gap & Portfolio Inputs
Target Deadline
Start Date & Age
Required Monthly Deposit
$331
Equivalent to ~$76 / week
Target Deadline
Sep 2036
120 months available
Contribution vs. Investment Growth Split
Current Assets
$100,000
Future Deposits
$39,765
Modeled Growth
$110,235
Investment growth is based on a constant modeled return (7%) minus annual fees (0.15%) and does not represent actual market performance.
Deadline Sensitivity: Impact of Shifting Target Date
12 Months Earlier
Sep 2035
$466 /mo
+$135 vs selected
Selected Target Date
Sep 2036
$331 /mo
12 Months Later
Sep 2037
$222 /mo
-$109 vs selected
Progress Milestone Timeline
Estimated dates to reach key percentage milestones of your Coast FIRE target ($250,000).
$62,500
Current Asset Base
$125,000
Dec 2028
Age ~32
$187,500
May 2033
Age ~36
$225,000
Jun 2035
Age ~38
$250,000
Sep 2036
Age ~40
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The Inputs That Define Your Coast FIRE Gap
The current gap depends on two numbers: your invested assets and your Coast FIRE target. Return, contributions and deadline determine how the model closes that difference over time.
Current Invested Assets
The portfolio value available today to count toward the selected Coast FIRE target.
Coast FIRE Target
The portfolio amount the user wants to reach before treating the gap as closed.
Target Deadline
The month and year by which the model attempts to reach the target.
Monthly Contribution
The recurring amount added to the portfolio during the catch-up period.
Net Investment Return
The modeled growth rate remaining after applying the calculator’s documented fee treatment.
Contribution Timing
Whether the recurring contribution is modeled at the beginning or end of each month.
Turn Your Coast FIRE Gap into a Plan in Three Steps
Enter the Target
Enter current invested assets and the Coast FIRE number you want to reach.
Choose Time or Contribution
Select a deadline to solve the required monthly contribution, or enter a contribution to solve the catch-up date.
Review the Milestones
Compare the gap, target-date result, contribution-and-growth split and projected progress milestones.
How the Coast FIRE Gap Calculation Works
Coast FIRE Target − Current Invested Assets = Current Gap
Current Assets + Future Contributions + Modeled Investment Growth = Projected Portfolio Value
First month projected value meets or exceeds Coast FIRE target = Estimated Catch-Up Date
The required-contribution solver and catch-up-date solver use the same shared future-value engine.
Understand Your Coast FIRE Gap Result
Current Gap
The dollar difference between current invested assets and the selected Coast FIRE target.
Progress Percentage
The percentage of the selected Coast FIRE target already represented by current invested assets.
Required Monthly Contribution
The modeled recurring contribution associated with reaching the target by the selected deadline.
Estimated Catch-Up Date
The first projected month when the portfolio meets or exceeds the selected target.
Total Future Contributions
The combined deposits included between today and the selected deadline or catch-up date.
Estimated Investment Growth
The projected value increase not explained by current assets or future deposits.
See How a Different Target Changes the Gap
Move the Coast FIRE goal to compare how the gap, required monthly contribution and estimated catch-up date respond.
Lower Target
Shrinks the dollar shortfall immediately and reduces the monthly contribution required for a fixed deadline.
Baseline Target
Maintains your standard retirement calculation and provides your core required monthly deposit and catch-up date.
Higher Target
Increases the required asset cushion, expanding the gap and extending the projected catch-up timeline.
Real-Time Interactive Synchronization
The goal slider inside the tool synchronizes with your typed numeric input. Moving the slider automatically recalculates the gap, progress percentage, required monthly annuity, and progress milestone dates.
Follow the Gap Through Each Progress Milestone
The milestone plan estimates when the portfolio may reach selected percentages of the Coast FIRE target under the current contribution and return assumptions.
Initial Asset Base
Establishes portfolio momentum early in the catch-up journey.
Halfway Threshold
Half of the Coast FIRE target is secured through deposits and growth.
Compounding Shift
Investment growth begins matching or exceeding monthly deposits.
Final Stretch
Within months of full Coast FIRE readiness.
Coast FIRE Reached
Gap fully closed. Portfolio grows to retirement target without further deposits.
How Much Would Be Required by Your Deadline?
The deadline solver calculates the monthly contribution associated with reaching the selected Coast FIRE target by the chosen month and year.
1. Available Timeline
Counts total months between today and your target deadline.
2. Asset Growth Offset
Projects how much your existing assets will grow by the deadline without extra deposits.
3. Required Annuity Deposit
Solves the remaining balance into an exact recurring monthly deposit requirement.
Mathematical Planning Result: The deadline solver determines the annuity payment required for compounding assets to reach the Coast FIRE target balance by your specified month and year.
The result is a mathematical planning estimate, not a contribution recommendation.
When Could Your Current Contribution Close the Gap?
The date solver projects the portfolio month by month and returns the first month when it meets or exceeds the selected Coast FIRE target.
1. Fixed Monthly Deposit
Applies your chosen monthly deposit at the beginning or end of each month.
2. Monthly Compounding
Applies the net monthly return rate each month to both existing assets and new deposits.
3. Target Crossing Date
Identifies the first calendar month and year when portfolio balance reaches or surpasses your target.
One Coast FIRE Gap from Today to the Target
Starting Point
Current Assets: $100,000
Target: $250,000
Current Gap: $150,000 (40% complete)
Catch-Up Period
Contribution: $1,000/mo
Net Return: 6.84%/yr
Duration: ~8 years 2 months
Target Result
Total Deposits: ~$98,000
Growth: ~$52,000
Target Met: $250,000+
The target is reached through a combination of current assets, future deposits and modeled investment growth. The relative contribution of each source changes with the deadline, return and monthly contribution.
When the Coast FIRE Gap Calculator Is Useful
You Already Know Your Coast Number
Use it when another calculator has produced a target and you want to measure the remaining shortfall.
You Have a Deadline
Use it to calculate the monthly contribution associated with a chosen target month and year.
You Know Your Contribution
Use it to estimate the first month when the current contribution may close the gap.
You Are Comparing Targets
Use the goal slider to compare how a higher or lower Coast FIRE number changes the catch-up plan.
You Want Milestones
Use it to estimate progress dates before the full Coast FIRE target is reached.
You Are Already Above Target
Use it to confirm the current surplus without generating an unnecessary required-contribution result.
Avoid These Coast FIRE Gap Calculation Mistakes
Using the Wrong Target
The result is only as relevant as the Coast FIRE number entered by the user.
Treating the Gap as Static
Investment growth and future contributions may change the shortfall over time.
Selecting a Past Deadline
A target date before the current month cannot be used for a future contribution plan.
Ignoring Fees
Investment fees reduce the net return used in the contribution and date calculations.
Mixing Contribution Timing
Beginning-of-month and end-of-month deposits produce different future-value results when return is not zero.
Calling the Required Amount Advice
The solver produces a mathematical equivalent and does not recommend a contribution level.
Ignoring Zero Return
When return is zero, the target must be closed entirely through current assets and future contributions.
Treating the Catch-Up Date as Guaranteed
The date depends on constant contribution and return assumptions that may not occur.
Model Limitations
Use the Right Calculator for the Next Question
Move between the main calculator, focused tools, and plain-English guides without changing the site experience.
Related Tools
Main Coast FIRE Calculator
ToolUse the shorter baseline when you only need the core Coast FIRE estimate.
Coast FIRE Calculator for Couples
ToolUse separate ages, balances, and contributions for a two-person household plan.
Coast FIRE Date Calculator
ToolSee the timeline to Coast FIRE and test how changing your contribution affects the crossing date.
Coast FIRE Calculator with Pension
ToolFocus on pension amount, start age, COLA, survivor percentage, and bridge years.
Related Guides
Coast FIRE Calculator Troubleshooting
GuideUnderstand unexpected Coast FIRE results: unchanged targets, inflation, contributions, return assumptions, input errors and differences between calculators.
What Is Coast FIRE?
GuideA complete introduction to Coast FIRE — what it means, how it works, and why it matters for your financial independence journey.
How Coast FIRE Works
GuideUnderstand the three phases of Coast FIRE: Build, Coast, and Retire. Learn how compound growth does the heavy lifting.
Coast FIRE Formula Explained
GuideLearn the Coast FIRE formula in simple terms. See what each number means, follow an easy example, and understand why age, return, inflation, and retirement spending change the result.
Coast FIRE Gap and Contribution Questions
What is a Coast FIRE gap?
The Coast FIRE gap is the difference between current invested assets and the selected Coast FIRE target. When current assets exceed the target, the calculator shows a surplus instead.
How does the Coast FIRE Gap Calculator work?
The calculator measures the current shortfall, then either solves the monthly contribution required for a deadline or estimates the first month when a selected contribution may close the gap.
How much should I contribute to close the gap?
The deadline solver calculates an estimated monthly amount using the current assets, target, time available, return, fees and contribution timing. It does not recommend a contribution level.
What happens when I do not select a deadline?
The calculator can still show the current gap and progress. To calculate an action result, choose a deadline or enter a monthly contribution for the catch-up-date mode.
What happens when the investment return is 0%?
The gap must be closed through current assets and future contributions because the model includes no investment growth. Beginning and end-of-month contribution timing produce the same result.
What if I am already above the Coast FIRE target?
The calculator displays a $0 gap, the current surplus and a $0 required monthly contribution. It does not recommend stopping retirement contributions.
Is the catch-up date guaranteed?
No. It is a planning projection based on constant contribution, return and fee assumptions. Actual investment performance and contribution changes may move the date.
Why does a shorter deadline require a larger contribution?
A shorter deadline provides fewer contribution periods and less time for modeled investment growth, so a larger recurring amount may be required to reach the same target.
Verified Sources & Methodology
IRC Sec. 72(t)(2)(A)(v) Early Distribution Exception
2026 Federal Brackets & Standard Deductions
Summary Plan Description (SPD) Distribution Rules
Retirement Claiming Ages (62–70)