FOBAS Calculator (Forgone Buy And Save)
Estimate how much a recurring expense could grow into if you redirect that money into investments each week.
What is a FOBAS calculator?
A FOBAS calculator helps you evaluate the long-term financial effect of a repeating expense. FOBAS stands for Forgone Buy And Save: instead of buying something frequently (coffee, snacks, app upgrades, delivery fees), you redirect that same amount into an investment account.
The core question is simple: “If I invested this recurring cost, what could it become?” This tool gives a practical answer using weekly contributions, compounding returns, and optional price inflation.
How this calculator works
Inputs used
- Cost per purchase: how much one purchase costs today.
- Purchases per week: frequency of the habit.
- Years to invest: total investing time horizon.
- Expected annual return: estimated growth rate of the invested money.
- Annual price increase: expected inflation in the habit’s price over time.
Calculation model
The calculator simulates weekly deposits. Each week it:
- Adjusts the purchase cost based on annual price growth.
- Multiplies by weekly frequency to get that week’s contribution.
- Adds the contribution to your balance.
- Applies weekly investment growth.
This approach is more realistic than a single static formula because it reflects consistent contributions and compounding behavior over time.
How to interpret the output
Key metrics you will see
- First-year habit cost: your current annual spending rate.
- Total redirected contributions: total cash you would invest over the selected period.
- Projected portfolio value: estimated value after compounding.
- Investment growth: gains generated by compounding above your contributions.
- Growth factor: how many times contributions grew.
Why FOBAS is useful
Small expenses are easy to ignore because each transaction is tiny. But repeated often, they become large annual cash flows. FOBAS reframes spending choices from short-term convenience to long-term opportunity cost.
This is not about perfection or never buying things you enjoy. It is about intentional tradeoffs: knowing what one habit costs today and what it might cost your future.
Best practices for realistic planning
Use conservative assumptions
- Try a return range (for example 5%, 7%, 9%) instead of a single optimistic number.
- Include price increase when the habit tends to inflate (coffee, subscriptions, transportation).
- Review your inputs every 3–6 months.
Combine with behavior design
- Automate transfers on payday.
- Create “intentional spend” days so cutbacks remain sustainable.
- Track one or two habits first, not everything at once.
Limitations and disclaimer
This calculator provides an educational estimate, not financial advice. Real returns vary, taxes and fees matter, and life rarely follows a perfect weekly schedule. Still, the directional lesson is powerful: recurring expenses plus time can significantly impact future wealth.