Plan Assumptions
Every assumption behind the Forbidden Finance retirement plan, with its default value, its allowed range, and how to change or reset it.
Overview
The retirement plan runs on assumptions: when you plan to retire, what your investments might return, what you spend. Each one starts from a default. Change any of them and the projection reruns with your numbers.
Available on: Pro and Premium. Assumptions in the Withdrawal and Simulation groups only affect the Premium sections.
Change an Assumption
Open Assumptions
On the retirement plan, tap Assumptions.
Edit a value
Each field shows its default and its allowed range. A field you have changed shows an Overridden badge.
Save
Tap Save. The plan reruns with your values.
To start over, tap Reset all and confirm. Every override returns to its default.
All Assumptions
Profile
| Assumption | Default | Range |
|---|---|---|
| Birth year | None, you enter it | 1900 to 2100 |
| Current age | Worked out from your birth year | Not editable |
| Country | US | US only for now. It decides which contribution limits apply. |
Timeline
| Assumption | Default | Range |
|---|---|---|
| Retirement age | 60 | 30 to 100 |
| Longevity age | 95 | 50 to 110. The projection runs to this age. |
Returns
| Assumption | Default | Range |
|---|---|---|
| Expected nominal return | 7.00%, or your FIRE budget's figure | 0% to 30% |
| Return volatility | 15.00% | 0% to 60%. Used by Monte Carlo. |
| Inflation | 3.00%, or your FIRE budget's figure | 0% to 20% |
| Fees drag | 0.00% | 0% to 5%. Fund and account fees, taken off the return. |
The plan works in today's money. It combines these into one real return: (1 + return − fees) ÷ (1 + inflation) − 1.
Spending
| Assumption | Default | Range |
|---|---|---|
| Annual expenses override | Empty: the plan uses your last three full months of spending, times 12 | 0 to 1,000,000,000 |
| Monthly contribution override | Empty: the plan uses your average monthly savings over the same months | 0 to 100,000,000 |
| Employer match per month | 0 | 0 to 10,000,000. Added to your monthly contribution. |
| Contribution growth (real) | 0.00% | −10% to 10% a year, after inflation |
FIRE variants
| Assumption | Default | Range |
|---|---|---|
| Withdrawal rate | 4.00%, or your FIRE budget's figure | 0.10% to 10% |
| Lean multiplier | 0.70 | 0.10 to 1.00 |
| Fat multiplier | 1.50 | 1.00 to 5.00 |
| Barista years | 0 | 0 to 40 |
| Barista monthly income | 0 | 0 to 10,000,000 |
Withdrawal (Premium)
| Assumption | Default | Range |
|---|---|---|
| Withdrawal strategy | Fixed real | Fixed real, Guyton-Klinger, or Variable percentage |
| Guardrail | 20.00% | 0% to 50%. Guyton-Klinger only. |
| Guardrail adjustment | 10.00% | 0% to 50%. Guyton-Klinger only. |
See Withdrawal Planning for what each strategy does.
Tax
| Assumption | Default | Range |
|---|---|---|
| Tax-deferred effective rate | 22.00% | 0% to 60%. Withdrawals from tax-deferred accounts are grossed up by this rate. |
Simulation (Premium)
| Assumption | Default | Range |
|---|---|---|
| Return model | Parametric lognormal | Parametric lognormal |
| Monte Carlo paths | 1,000 | 100 to 5,000 |
Frequently Asked Questions
Where do the defaults come from?
Most are fixed starting points. Three follow your FIRE budget when you have one: expected return, inflation, and withdrawal rate. Annual expenses and monthly contribution come from your own transactions until you type your own figures.
Is my birth year stored safely?
Yes. Your birth year and every money amount in your plan are encrypted, like the rest of your financial data.
Do assumptions change anything outside the plan?
No. They only feed the retirement projection and the FI Progress and Coast FIRE dashboard cards.
Related Articles
Retirement Plan
What the plan shows and how to read it.Monte Carlo Simulation
How volatility and path count are used (Premium).Withdrawal Planning
Strategies, guardrails, and income sources (Premium).Need more help? Email us at [email protected] and we will get back to you.