Planning explainer
How to Choose Inflation Assumptions Without CPI
You can choose inflation assumptions without CPI by using your own bills and ranges. You are not predicting inflation. You are choosing planning inputs for your basket so you can see how sensitive your costs are. This keeps the process about personal inflation inputs, not forecasts.
Published: December 30, 2025 · Updated: December 30, 2025 · By FinToolSuite Editorial
Disclaimer
- Educational purposes only, not financial advice.
- Examples are illustrative and simplified.
- Results depend on your inputs and assumptions and are not guaranteed.
- This page does not predict future inflation and does not provide forecasts.
- See the Privacy Policy for handling details.
Open the personal inflation basket calculator
Set low, base, and high inputs for each category and see how the weighted average responds.
Quick answer
- Use ranges, not one perfect number.
- Start with low, base, and high assumptions for each category.
- Sanity check against your own recent bills.
- Save scenarios and compare.
Why you can choose inflation assumptions without CPI
CPI is an average basket, not your basket. Your goal is planning sensitivity, not forecasting. The calculator shows how your mix behaves when you change assumptions. For a refresher on how personal baskets differ from CPI, see the personal inflation vs CPI guide.
The low base high method
Use three bands per category so you see the range of outcomes instead of clinging to one guess. This keeps your personal inflation inputs flexible.
| Category | Low | Base | High | Notes |
|---|---|---|---|---|
| Housing | 2% | 4% | 6% | Use renewal notice if available. |
| Food | 3% | 5% | 8% | Check recent receipts totals. |
| Utilities | 1% | 3% | 5% | Average the last three months. |
| Transport | 2% | 4% | 7% | Account for fuel or pass increases. |
How to use your own bills safely
You can build inputs from your bills without sharing personal documents. Keep it simple and consistent.
- Use totals, not item level data.
- Average the last three months for variable bills.
- Use renewal notice percent changes when you have them.
- Convert annual bills to monthly equivalents so weights add up.
- Keep a note of assumptions but avoid storing sensitive details.
Read more in how to estimate annual bills in your basket.
Avoid common traps
- Do not copy a headline number as your personal rate.
- Do not assume last month repeats forever.
- Do not mix weekly and monthly spend in one basket.
- Do not treat outputs as guaranteed.
- Avoid false precision like 4.37 percent if you are guessing.
One worked example with round numbers
This example shows how one category change can move the personal rate. The numbers are simple so you can follow the math.
| Category | Weight | Base inflation | Contribution points |
|---|---|---|---|
| Housing | 50% | 4% | 2.0 |
| Food | 30% | 5% | 1.5 |
| Transport | 20% | 3% | 0.6 |
The weighted average here is 4.1%. If housing rises to 6% while weights stay the same, housing contribution becomes 3.0 and the total moves to 5.1%. Small changes in big categories matter more than shifts in small categories.
Nominal vs real in brief
Nominal numbers are the cash amounts. Real numbers adjust for purchasing power after inflation. Read the nominal vs real explainer to see how the difference affects your plan.
How to use scenarios in the tool
Create a Base scenario with your best estimates. Create a High stress scenario with larger increases in key categories. Compare projected costs side by side to see your range.
Open the personal inflation basket calculatorFAQ preview
What inflation percent should I use?
Pick low, base, and high percents from your own bills to see a range.
Is CPI required?
No. CPI is a broad average. Use your own costs for your basket.
Should every category have the same rate?
Give each category its own range. They move differently.
How often should I update assumptions?
Update when your bills change or every few months.
Why does my personal inflation feel higher?
Your mix can differ from a headline rate, and big categories can push it up.
Can I compare scenarios?
Yes. Save Base and High, then compare in the calculator.
Is this financial advice?
No. It is educational and depends on your inputs; outputs are estimates.