Calculate your real current spending — not your estimate
Pull three months of actual bank and card data before calculating your FI number — estimates are reliably too low.
Key takeaways
- What it is: Pull three months of actual bank and card data before calculating your FI number — estimates are reliably too low.
- Why it works: People consistently underestimate their spending due to availability bias: salient, large purchases are easy to recall while small recurring expenses are invisible. The average person underestimates food, entertainment, and miscellaneous spending substantially. A FI number built on an underestimated baseline produces a retirement plan that runs out of money — not from investment failure but from spending reality that was never honestly captured.
- Evidence: Backed by observational / correlational evidence.
- Avoid: Building the FI number on "what I plan to spend in retirement" rather than current actual spending — retirement spending projections are even less reliable than current spending estimates.
Why it works
People consistently underestimate their spending due to availability bias: salient, large purchases are easy to recall while small recurring expenses are invisible. The average person underestimates food, entertainment, and miscellaneous spending substantially. A FI number built on an underestimated baseline produces a retirement plan that runs out of money — not from investment failure but from spending reality that was never honestly captured.
How to do it
- 1Download three to six months of bank and all credit card statements.
- 2Categorize every transaction, including irregular or "one-time" items (these recur annually).
- 3Annualize all irregular spending: car registration, insurance lump sums, travel — divide by 12.
- 4Add 10-15% as an irregular-expense buffer; life consistently costs more than the line items suggest.
What the evidence says
ObservationalMemory-based spending estimates are reliably lower than actual measured spending, consistent with availability bias and motivated underestimation. The discrepancy is documented across financial behavior research.
Honest caveat: Studies on spending estimation error use samples that may not represent high-income earners with complex spending; the direction of the bias (underestimation) is consistent.
Common mistake
Building the FI number on "what I plan to spend in retirement" rather than current actual spending — retirement spending projections are even less reliable than current spending estimates.
IX Coach walks you through a structured spending audit that surfaces the invisible recurring expenses most FI calculators miss, giving your number a realistic foundation.
Practice this with IX Coach →