Comprehensively control metered utility bills. This is now free because I don't have the time to fully update it: it will eventually be replaced with a more sophisticated general billing app.

This app allows you to check [and manipulate] your gas and electricity bills to all levels of complexity.
Dual tariffs are allowed, to accommodate a change over; or to directly compare 2 tariffs

3 types of Gas meter are allowed for, with the associated Calorific values. Tier1 tier2 and Off-peak[latter only for Electricity] are allowed for.
3 Tier 1 limit types are incorporated. 8 Standing charge types.
There are up to 6 discounts, applicable Net or Gross; with 10 discount types available.
Key comparison indicators have been added: kWh per day and Cost per kWh (gross).

Utility providers may delight in insanely complicated tariffs but here is the answer!

It has its own internal help screens, backed up by my website.

Save and Restore multiple bills. Also use tools to cost projected increases in use/time/tariffs and generally manipulate billing.
Extend your current bill to a year (with one button) and use totals.

Calculate your correct bill.

Charges are calculated to 2 decimal places: for standing charges [dates] and volumetric charges [readings].
VAT [Sales Tax] can be added or removed.