ahorr.ai · Blog
Indexed vs Fixed Tariff: The Forensic Comparison for Your Electricity Bill
Respuesta rápida
Choosing between an indexed and a fixed tariff depends on whether you prefer market-linked savings or price stability. In the Spanish electricity market, indexed rates fluctuate with wholesale prices while fixed rates offer a constant price per kWh. To optimize your bill, analyze your consumption patterns and risk tolerance before switching providers.
En 30 segundos
- ✓Locate the 'Power Contracted' (Potencia) section to see if you are overpaying for capacity.
- ✓Identify the 'Cost per kWh' or 'Energy' line to find your current rate.
- ✓Check for 'Vampire Services' like hidden insurance or maintenance fees.
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Transparencia y fuentes
Authorship, methodology and official sources.
Actualizado: 10 de enero de 2026
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Transparencia y fuentes
Authorship, methodology and official sources.
Actualizado: 10 de enero de 2026
Autoría
Equipo ahorr.ai
Auditoría energética (España)
Metodología orientada a decisión: separar coste fijo/variable, detectar extras y comparar opciones con números claros.
Metodología
- →Separamos coste fijo (potencia/término fijo), energía y cargos/impuestos.
- →Buscamos sobrecostes típicos: potencia sobredimensionada, servicios extra, lecturas estimadas.
- →Damos pasos accionables (qué tocar primero) con ejemplos orientativos, no promesas.
- →Enlazamos fuentes oficiales y marcamos lo que puede variar por comercializadora.
Información orientativa (España). Comprueba condiciones con tu comercializadora: precios, peajes, cargos e impuestos pueden variar.
The difference between options (applied to tarifa indexada vs fija)
Understanding the core difference is the first step in your energy autopsy.
What they sell you vs what you pay
Marketing often highlights a low kWh price but hides the 'management fee' or the cost of power. In a fixed rate, you pay for stability; in an indexed rate, you pay for transparency.
The trap of comparing only kWh
Focusing only on the energy price ignores the fixed terms and 'vampire' services that can inflate a bill by 20% without you noticing.
Decision matrix (when each one suits you)
Your lifestyle dictates which tariff will actually save you money.
If you consume at peak hours
If your home is most active between 10 AM and 2 PM, a fixed rate usually protects you from the highest market prices.
- ✓Ideal for families with standard schedules
- ✓Better for those who don't want to check daily prices
- ✓Provides a 'ceiling' for your monthly expenses
If you can move consumption to off-peak
If you can program your dishwasher or charge an EV at night, the indexed rate is almost unbeatable.
- ✓Best for tech-savvy users
- ✓Significant savings during spring and autumn
- ✓Requires monitoring market trends
Risks and small print (in human)
Every contract has shadows. Here is how to shine a light on them.
Volatility
Indexed rates are tied to the wholesale market. If there is a geopolitical crisis, your bill will reflect it immediately.
Permanence and extras
Many 'cheap' fixed rates come with a 12-month commitment or mandatory maintenance services that negate any savings.
How to decide with your real consumption (without 'opinionitis')
Stop listening to neighbors and start looking at your data.
What data your bill provides
Your bill contains your hourly consumption curve. This is the 'DNA' that tells you exactly if an indexed rate would have been cheaper last month.
CTA to audit
Don't do the math manually. A forensic audit can process these thousands of data points in seconds.
Checklist: Indexed vs Fixed Decision Matrix
- ✓Locate the 'Power Contracted' (Potencia) section to see if you are overpaying for capacity.
- ✓Identify the 'Cost per kWh' or 'Energy' line to find your current rate.
- ✓Check for 'Vampire Services' like hidden insurance or maintenance fees.
- ✓Verify your peak usage vs. contracted power in the consumption graph.
- ✓Check for 'Permanence' clauses that might penalize you for switching.
Decision Matrix: Indexed vs Fixed
| Consumer Profile | Recommended Tariff | Main Advantage | Main Risk |
|---|---|---|---|
| The Optimizer (Shifts loads) | Indexed | Pays market price during low demand | Sudden market spikes |
| The Stable Budgeter | Fixed | Predictable monthly cost | Paying a premium for 'peace of mind' |
| The High-Power User | Fixed (with power optimization) | Avoids volatility on high volume | Hidden 'vampire' services in the contract |
Estimates based on standard Spanish market profiles.
The Landlord's Hidden Leak
A landlord in Madrid was puzzled by a €140 bill for a small rental apartment. The tenant was on an indexed rate but had no idea about the 'Valle' hours, performing all heavy chores during peak times.
Hallazgos
- ✓4.6 kW contracted power while the peak never exceeded 2.8 kW
- ✓A €6.99/month 'emergency' maintenance service never requested
- ✓Effective price of €0.23/kWh (including taxes) due to peak-hour cooking
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Related guides
Preguntas frecuentes
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We process your data ephemerally. No spam, no commercials, just the truth about your energy costs.
Disclaimers
- Informational tool; not financial advice.
- We don’t guarantee savings: these are estimates.