Troubleshooting
Cost of Delay Calculator: Common Mistakes
Most surprising results come from input assumptions—rate format, delay units, or horizon—rather than the tool itself. Here are the top mistakes and quick fixes.
Published: December 22, 2025 · Updated: December 22, 2025 · By FinToolSuite Editorial
Check your inputs in the calculator
Reset with clean inputs and rerun start-now vs start-later.
Quick answer
If the cost of delay looks too big or too small, check rate format (5 vs 0.05), delay units (months vs years), the horizon/end date, and whether your rate is gross or net of fees.
Picking a return assumptionDisclaimer
Educational purposes only; not financial advice. Examples are illustrative; real returns vary and investments can go down as well as up. Fees, taxes, inflation, and provider rules vary by country and account type.
Top 10 mistakes (and fixes)
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Entering 5 instead of 0.05.
Why: Percent vs decimal flips the rate. Fix: Enter rates as percents (5 for 5%).
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Using an optimistic rate as if it were guaranteed.
Why: High inputs inflate projections. Fix: Run low/base/high scenarios; don’t treat any rate as certain.
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Confusing “interest rate” with “return assumption.”
Why: Savings rates vs investment returns are different contexts. Fix: Use a realistic assumption for the product you’re modeling.
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Picking the wrong delay unit.
Why: Entering 6 months as 6 years skews the gap. Fix: Use months where expected; convert to years if you calculate manually.
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Changing the horizon unintentionally.
Why: Different end dates make comparisons uneven. Fix: Keep the same horizon for start-now and start-later.
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Changing multiple variables at once.
Why: Hard to tell which input caused the change. Fix: Vary one input (like delay) while holding others constant.
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Ignoring fees.
Why: Gross vs net return differs. Fix: Lower the rate to approximate fees if needed.
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Ignoring inflation.
Why: Nominal gains may overstate purchasing power. Fix: Consider a lower “real” rate if you want an inflation-adjusted view.
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Expecting the cost to be linear.
Why: Compounding effects often grow over time. Fix: Check charts/tables to see how the gap widens across the horizon.
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Forgetting outcomes vary in reality.
Why: Real returns can be volatile. Fix: Treat outputs as estimates; test multiple scenarios.
Mini sanity-check example
£5,000, 5% (0.05), delay 12 months, horizon 15 years. Checklist: rate is in percent, delay is in months/years correctly, horizon is the same for both scenarios.
Try this in the toolWhere to go next
FAQ
Why does my cost of delay look huge?
Check rate format, delay units, and horizon. High rates or long delays can widen the gap quickly.
Why does my cost of delay look small?
Short delays, low rates, or short horizons shrink the gap. Confirm inputs and units.
Should I use 5 or 0.05 for the rate?
Use 5 for 5% in the calculator (percent format).
What’s a “return assumption”?
It’s a rate you pick for modeling; it’s not guaranteed. See the return assumption guide for tips.
Does compounding frequency matter?
It can change both paths slightly. Keep frequency the same across scenarios.
Does inflation change the result?
Yes. Higher inflation reduces real purchasing power. Consider a lower “real” rate if you want that view.
How do fees affect cost of delay?
Fees lower net returns. You can model them by reducing the rate input.
Are calculator results guaranteed?
No. They’re estimates based on your inputs; real outcomes can differ.
How do I compare 6-month vs 12-month delays?
Keep the same amount, rate, horizon, and frequency. Change only the delay and compare side-by-side.
Final CTA
Save three scenarios: start now, start in 6 months, and start in 12 months. Compare the estimated cost of delay side-by-side.