What is the Cash vs Investing Opportunity Cost Calculator?
The Cash vs Investing Opportunity Cost Calculator helps you understand the long-term cost of holding money in cash instead of investing it. It compares cash savings against investing over time and shows how inflation, tax and compounding affect your wealth in both nominal terms and real spending power.
How the Calculator Works?
This calculator compares two parallel paths using the same starting amount and contributions. One path assumes money is held in cash, earning interest and subject to UK savings tax rules. The other assumes the money is invested, with growth reduced by fees and any applicable tax depending on the investment wrapper used.
It compounds values monthly, adjusts for inflation and shows both headline balances and real (inflation-adjusted) values. By running both paths side by side, the calculator highlights the opportunity cost of choosing cash, how long it takes cash to fall behind, and whether it ever catches up.
Step One: Enter Your Starting Amount and Time Horizon
Add your lump sum, optional monthly contributions and how long you plan to hold the money.
Step Two: Set Cash and Investing Assumptions
Enter interest rates, tax band and inflation for cash. Set expected investment returns, fees and choose whether the investment is held in an ISA, pension or taxable account.
Step Three: Compare Outcomes and Opportunity Cost
Review balances over time, opportunity cost in pounds and percentage terms, and see how inflation affects purchasing power.
Disclaimer: This calculator provides illustrative projections only and does not constitute financial advice. Investment returns, interest rates, inflation and tax rules can change. Consider professional advice before making long-term financial decisions.
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What is the Cash vs Investing Opportunity Cost Calculator?
It is a UK-specific tool that compares cash savings and investing to show the long-term cost of holding cash after inflation, tax and compounding.
What does “opportunity cost” mean here?
It is the difference between what your money could have grown to if invested versus what it becomes when left in cash.
Why does inflation matter so much?
Inflation reduces purchasing power over time. Even when cash balances grow, their real value may fall once inflation is taken into account.
Does this include UK savings tax rules?
Yes. Cash interest is taxed based on the Personal Savings Allowance for your income tax band.
Are ISAs treated differently from other investments?
Yes. Investments held in a Stocks and Shares ISA are modelled as tax-free, while GIAs can include a simplified tax drag.
Can cash ever beat investing?
Over short periods or during market downturns, yes. Over longer time horizons, investing has historically provided higher real returns, though outcomes are never guaranteed.
What is the breakeven point?
It is the point at which the investing balance overtakes cash, after accounting for inflation, tax and fees.
Are the results shown in today’s money?
Yes. You can toggle between nominal values and real values adjusted for inflation.
Does this assume regular contributions?
You can model a one-off lump sum, regular monthly contributions, or both.
Is my data stored?
No. All calculations run locally in your browser and no data is sent or saved externally.