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Example data table
Sample scenarios to help you sanity-check inputs.
| Home type | Annual usage (kWh) | Current rate | New rate | Standing/day | Period |
|---|---|---|---|---|---|
| Small apartment | 8,000 | 0.080 | 0.070 | 0.20 | 12 months |
| Average home | 12,000 | 0.075 | 0.062 | 0.25 | 24 months |
| Large home | 18,000 | 0.078 | 0.066 | 0.28 | 36 months |
Formula used
- Monthly usage: Annual kWh ÷ 12
- Monthly days: 365 ÷ 12
- Escalated rate (month m): Rate × (1 + escalation%)^(m/12)
- Monthly cost: (kWhₘ × rateₘ + daysₘ × standingₘ) × (1 + VAT%)
- Total cost: Sum of monthly costs over the period
- Total savings: Current total − (New total + exit fee + switching cost)
- Break-even month: (exit fee + switching cost) ÷ average monthly savings (if savings > 0)
How to use this calculator
- Enter your annual gas usage from a recent bill in kWh.
- Set the comparison period to match the offer term.
- Add your current unit rate and daily standing charge.
- Enter the new offer’s unit rate and standing charge.
- Include expected annual changes if prices may rise or fall.
- Add any exit or switching fees, plus applicable tax/VAT.
- Click Calculate Savings and review totals and break-even timing.
- Download CSV for detail or PDF for a quick shareable summary.
What the comparison measures
This calculator estimates your bill difference by combining energy charges and daily standing charges. You enter annual gas use in kWh, then the tool spreads usage across months and applies each tariff’s unit rate. Taxes or VAT are applied to both components, so you compare totals fairly.
How costs are projected over time
Many tariffs change during a contract. The annual change field models escalation or decline using a compounding factor each month. For example, a 3% annual change increases the effective unit rate slightly every month, which can materially affect 24 or 36 month decisions when rates are close. If you expect a price cap or indexed pricing, set values that match your assumption.
Interpreting savings and break-even
Savings are calculated as current total minus new total, then reduced by one-time exit and switching fees. If fees exist, break-even estimates how many months of average monthly savings are needed to recover them. A break-even beyond your chosen term suggests switching may not pay back. Example: a $60 exit fee and $5 monthly savings implies about 12 months to recover costs.
Sensitivity to usage and standing charges
Higher consumption amplifies unit-rate differences, while lower consumption makes standing charges relatively more important. As a quick check, compare the standing charge lines first: if the new daily charge is higher, a low-usage home may see smaller gains even with a cheaper unit rate. For a 0.05 daily increase, the added annual cost is roughly 18.25 in your currency.
Using results for decision-making
Use the month-by-month table and chart to spot periods where savings widen or narrow as escalation compounds. Export CSV to share with an advisor, or keep the PDF summary for records. Re-run scenarios with seasonal usage assumptions if your winter demand is significantly higher than summer. For example, test 20% higher usage to stress-check your budget before committing to a longer term.
FAQs
1) Should I use kWh from one bill or a year?
Use annual kWh from your supplier statement if possible. If you only have one bill, convert it to yearly usage by dividing by billed days and multiplying by 365, then recheck against typical seasonal changes.
2) What if my usage is seasonal?
This tool spreads usage evenly across months for clarity. If your winter consumption is much higher, run scenarios by increasing annual kWh or shortening the term to the heating season, then compare outcomes.
3) Do standing charges really matter?
Yes. Standing charges apply every day, even with low usage. For small apartments or mild climates, a higher standing charge can offset a cheaper unit rate, so compare both components together.
4) How does annual change affect results?
The calculator compounds the annual change monthly. Over longer terms, small differences in escalation can outweigh a slightly better starting rate, especially when your usage is high or fees are minimal.
5) What does break-even month mean?
It estimates how long it takes for monthly savings to repay one-time costs like exit fees and switching fees. If break-even occurs after your comparison period, the switch may not be cost-effective.
6) Are taxes and VAT applied correctly?
Tax/VAT is applied to the combined energy and standing charge totals each month. If your bill taxes only certain items, set VAT to zero and include any fixed taxes as part of the standing charge.