UK Fin Lab

Professional-grade UK financial tools

BILLS

Fix vs Variable Comparison

Compare fixed and variable household energy tariffs to see which option may cost less over your chosen time period. Enter your estimated usage, tariff rates and your best guess for how variable prices may change.

Enter your tariff details

Useful for comparing shorter fixes as well as a full 12-month view.

Set gas to 0 for an all-electric property.

Leave as 0 unless you want to factor in likely exit fees.

Use negative numbers if you expect prices to fall.

Cheaper option Fixed tariff
Fixed tariff cost £1,759.75
Variable tariff cost £1,767.65
Difference £7.90

Result summary

The fixed tariff looks cheaper by £7.90 over 12 months based on your usage and expected variable price changes.

Cost breakdown

Item Fixed tariff Variable tariff
Electricity usage £702.00 £708.75
Gas usage £747.50 £748.65
Standing charges £310.25 £310.25
Exit fees £0.00 £0.00
Total £1,759.75 £1,767.65

Assumptions used

Comparison period 12 months
Electricity usage modelled 2,700.00 kWh
Gas usage modelled 11,500.00 kWh
Fixed electricity rate 26.00p/kWh
Fixed gas rate 6.50p/kWh
Variable electricity effective rate 26.25p/kWh
Variable gas effective rate 6.51p/kWh
Days charged 365

How to interpret this

  • Variable rates are modelled using your current rate adjusted by the percentage change you enter for the period.
  • Usage is spread evenly across the comparison period, so this does not model seasonal winter-heavy consumption.
  • Standing charges are applied across the estimated number of days in the chosen number of months.
  • Use this as a decision aid rather than a precise supplier bill forecast.

How this fixed vs variable comparison works

This calculator spreads your annual electricity and gas usage across the comparison period, then works out the estimated total cost for a fixed tariff and a variable tariff. For the variable option, it applies your expected percentage change to the current unit rates.

When this tool is useful

It is useful when deciding whether to lock into a fix now, stay flexible on a variable tariff, or sense-check whether a quoted fix looks competitive against your current deal over the next few months.

What to keep in mind

  • Variable tariffs can move up or down, so the result depends on the percentage change you enter.
  • Standing charges matter, especially for lower-usage homes.
  • Exit fees can make a fix less attractive over shorter periods.
  • Real bills can differ because of regional pricing, direct debit smoothing, discounts and tariff changes during the period.