Coast FIRE Calculator
Estimate when modeled savings could grow to a retirement target without further contributions, using a constant annual return and year end deposits.
How It Works
Enter current age, starting savings, expected annual return, retirement age, target, and annual contribution. The model grows the current balance each year and adds the entered contribution at year end until the balance first reaches the coast test. That test asks whether the balance at that age can grow to the target by retirement without later contributions.
The age table begins with current savings and ends at retirement age. In each row, the contribution column indicates whether a contribution is planned at the end of the following year. A deposit may be added in the final modeled year when the coast test is first met at retirement age. The monthly savings result is a separate level contribution benchmark across the full remaining horizon, divided by 12.
Total contributions sum the deposits made before coast age. Compounding gain is the retirement age balance minus starting savings and those deposits, so the three amounts reconcile to the projected retirement balance.
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Step by step
- Enter age, savings, return, retirement age, target, and annual contribution
- Review Coast FIRE age and year by year projection table
- Adjust contribution or return to pull coast age forward or backward
Worked example
Start at age 30 with $0 saved, a 0% annual return, retirement at age 35, a $50,000 target, and a $10,000 annual contribution.
At 0% return, the model adds $10,000 at each year end and reaches $50,000 at age 35. It reports age 35 as the coast age because the balance then meets the target, with no deposits after the final row. The monthly savings benchmark is $833.33 across five years. The projection uses fixed assumptions and is not a forecast.
When to use this calculator
Use Coast FIRE Calculator to estimate when the modeled balance could reach a retirement target without later contributions under the entered assumptions.
Common mistakes
Read the contribution column as a plan for the following year, not as a deposit already included in that row’s balance. The current age row shows starting savings, and the retirement age row shows the final modeled balance.
Running a single baseline scenario ignores tail risks.
The Formula
At each age: projected value without future contributions = balance × (1 + r)^(retirement age − age). Coast age is the first age when this value reaches the target. Before coast: next balance = balance × (1 + r) + annual contribution at year end. After coast: next balance = balance × (1 + r). Monthly savings needed for target = level annual contribution needed over the full remaining horizon divided by 12.
The current age row shows starting savings. Each age row indicates whether a contribution is planned at the end of the following year. Growth is annual and contributions are added at year end while the coast test has not been met, including the final modeled year if needed to reach the target at retirement. No deposit occurs after the retirement age row. The monthly savings benchmark is calculated separately. Values are rounded to cents.
Limitations and assumptions
This projection assumes a constant annual return and contribution, annual growth, and contributions added at year end. It does not model taxes, fees, inflation, withdrawals, changing contributions, or market variability. The monthly savings figure is a level contribution benchmark across the full remaining horizon. The result is a mathematical scenario, not a retirement forecast or investment advice.
Key terms
- How is Coast FIRE age calculated
- The first age when the projected balance, with no later deposits, can grow to the target by retirement age.
- What if Coast FIRE age shows as not reached
- No age met the coast test using the entered annual contribution, return, target, and retirement age.
- Model assumption
- Projected retirement age balance minus starting savings and modeled contributions.
Compare alternatives
Compare the coast milestone with a full savings timeline using Time to FIRE. Barista FIRE can model a part time work scenario. Each calculator uses its own assumptions, so enter matching spending, returns, and contributions when comparing results.
Try a lower annual return or contribution to see how sensitive the coast age is. The monthly savings benchmark is calculated separately from the annual contribution used in the year by year projection.
FAQ
How is Coast FIRE age calculated?
The model grows the balance each year and adds the entered annual contribution at year end while the coast test has not yet been met. Coast age is the first age when the resulting balance can grow to the target by retirement without later contributions. The final modeled year can include a contribution when the coast test is first met at retirement age; there are no deposits after the final row.
What if Coast FIRE age shows as not reached?
Not reached means the balance produced by the entered annual contributions does not meet the coast test by retirement age. The year by year table still shows that projected balance at retirement. The monthly savings figure is a separate level savings benchmark for reaching the target over the full remaining horizon.
What does compounding gain represent?
Compounding gain is the retirement age balance minus starting savings and modeled contributions. Together, starting savings, contributions, and compounding gain reconcile to the projected retirement age balance. It is the model’s growth amount, not a separate market return forecast.
Do I still need income after Coast FIRE?
Coast FIRE describes a retirement savings milestone, not permission to stop working. This calculator does not model the income needed to cover current expenses before the selected retirement age.
How can I bring Coast FIRE date sooner?
The coast age changes when you change starting savings, annual contribution, expected return, target, or retirement age. The model holds the annual return and contribution amount constant and does not include taxes, fees, inflation, or changing deposits.
Related Tools
Use Time to FIRE to examine a timeline that continues monthly saving, Barista FIRE to model part time income, and Lean vs Fat FIRE to compare different spending targets. Match assumptions when comparing tools; their results answer different planning questions.