BillSave Adds Great Britain, CSV Uploads and NEM12 Support

IAMMETER BillSave can now calculate and compare supported electricity offers in Great Britain as well as Australia. This release also opens BillSave to people who do not have an IAMMETER meter or an IAMMETER Cloud Site: users can upload their own interval energy data and apply supported tariffs to the same measured usage profile.

BillSave now accepts three energy-data sources:

interval energy from an authorised IAMMETER Cloud Site;
a BillSave interval CSV uploaded by the user;
an AEMO MDFF NEM12 v2.7 file in the Australian market.

All three sources enter the same Billing Engine. Users can calculate one offer with Run Bill, compare up to five selected offers with Compare Offers, or use Find Best to rank the supported offers that can be calculated with the selected data and confirmed parameters.

Great Britain Is Now Available in Limited Beta

BillSave now supports the Great Britain electricity market, covering England, Scotland and Wales. Northern Ireland is not currently included because it operates under a different electricity-market structure.

Electricity prices in Great Britain are not treated as one national rate. BillSave represents the 14 GSP Group regions, their DNO and IDNO context, GBP currency, the Europe/London timezone and British Summer Time transitions. Regional tariff versions can therefore use the unit rate and daily standing charge that apply to the selected area.

The initial limited-Beta catalog contains three residential product families:

Octopus 12M Fixed August 2026 v6 — a single-rate, 12-month fixed product paid by Monthly Direct Debit;
Octopus Go 12M Fixed — a two-rate smart tariff with a five-hour lower-price period from 00:30 to 05:30 local time each day;
Co-op 12M Fixed — a single-rate, 12-month fixed product supplied through the Octopus platform but represented under Co-op Energy as the Supplier.

Each product family currently has 14 regional tariff versions, for a total of 42 Great Britain Tariff versions. The catalog presently covers Octopus Energy and Co-op Energy; it is not a complete list of every Supplier or electricity tariff available in Great Britain.

Search the supported Great Britain offers to review their regions, rates, eligibility information and official sources.

Compare an EV Tariff with Actual Half-Hourly Usage

The timing of consumption can matter as much as the total amount of electricity used. Octopus Go, for example, currently has a lower-price period between 00:30 and 05:30 local time. A household that regularly charges an electric vehicle during that period may receive a different result from one whose main consumption occurs earlier in the evening.

BillSave applies the tariff schedule to the measured intervals in the selected billing period. Schedule evaluation uses Great Britain local time and accounts for British Summer Time changes rather than treating every timestamp as a fixed UTC clock time.

Octopus Go also has eligibility requirements. A calculation does not confirm that a user can join the tariff. Users should verify that they have a compatible smart meter, meet the electric-vehicle conditions and satisfy the Supplier's current terms before making a decision.

Ofgem Price Cap Is Shown as a Reference

BillSave includes the regional Ofgem residential single-rate Direct Debit Price Cap rates for the third and fourth quarters of 2026 as reference data.

The Price Cap is not a Supplier Offer. It cannot be selected as a product to switch to and does not participate in the supported-offer ranking. Its purpose in BillSave is to provide regional regulatory context when users review an estimated result.

Upload Energy Data Without an IAMMETER Device

An IAMMETER Cloud Site is no longer required to calculate an offer in BillSave. A user can export interval data from another smart meter, energy portal or monitoring system, convert it to the BillSave CSV format and save it as a private Dataset.

IAMMETER sign-in is still required. It identifies the user's private BillSave workspace so that Datasets, confirmed parameters, calculation Runs and reports remain available after changing browser or signing in again. Uploading a Dataset does not authorise or require access to an IAMMETER Cloud Site.

The simplest BillSave CSV contains one row per interval:

start_at,end_at,import_kwh,export_kwh
2026-08-01T00:00:00+10:00,2026-08-01T00:30:00+10:00,0.420,0.080
2026-08-01T00:30:00+10:00,2026-08-01T01:00:00+10:00,0.390,0.060

The format supports real 5, 15 or 30-minute intervals, grid import, grid export and an optional controlled-load channel. Timestamps must contain an explicit UTC offset. BillSave checks the offsets against the Dataset timezone, including repeated or missing local times during Great Britain daylight-saving transitions.

Before saving anything, Preview reports the interval length, time coverage, import and export totals, gaps, overlaps and available quality information. A Dataset can be saved only after the required checks and confirmations are complete.

Read the upload guide or download the BillSave CSV template.

Australian Users Can Upload NEM12

In Australia, BillSave can now import uncompressed UTF-8 files that follow AEMO MDFF NEM12 v2.7. It validates the applicable 100, 200, 300, 400, 500 and 900 records and accepts real 5, 15 or 30-minute interval data.

A NEM12 file may contain several data streams, and a stream name or NMI suffix does not always identify its billing direction reliably. BillSave therefore requires the user to map every kWh stream explicitly as:

Grid import;
Grid export;
Controlled Load import; or
Ignore.

BillSave does not guess the direction. It also reads NEM12 quality records so Actual, Estimated and Substituted data can remain visible in the Dataset and calculation quality.

NEM12 upload is currently available only in the Australian market. ZIP archives are not accepted, and users must confirm every billing stream before saving the Dataset.

Preserve the Real Interval Resolution

BillSave retains real 5 and 15-minute source data while also creating deterministic 30-minute aggregates when an offer uses a coarser billing interval.

Five-minute data can be aggregated to 15 or 30 minutes.
Fifteen-minute data can be aggregated to 30 minutes.
Thirty-minute data is never divided into invented 5 or 15-minute values.
Fifteen-minute data is never divided into invented 5-minute values.

This matters for dynamic or wholesale-linked tariffs that may require genuine fine-resolution data. A lower-resolution source cannot safely reproduce price changes that occurred inside the original interval.

Use the Same Dataset for a Fair Comparison

When an uploaded Dataset is saved, BillSave creates an immutable Dataset Revision containing the normalised intervals, source and format information, coverage, quality, confirmed channel mapping and content hashes. Changing a NEM12 stream mapping creates a new Revision instead of rewriting the input used by a historical calculation.

The same Dataset Revision and billing period can then be used for Run Bill, Compare Offers and Find Best. This keeps the energy input fixed while the tariff rules change, avoiding a comparison in which different offers are calculated from different dates or energy data.

Incomplete or low-quality input may produce an Estimated result or prevent a complete calculation. BillSave does not silently turn a missing day into zero consumption or claim a definitive lowest cost when the required data is unavailable.

Start with Your Own Energy Data

BillSave calculations are estimates for comparison, not Supplier or retailer invoices, settlement statements, financial advice or a switching service. Catalog availability does not guarantee eligibility, and users should confirm current official terms before acting on a result.

Open IAMMETER BillSave to choose Australia or Great Britain, or follow the complete BillSave calculation and comparison guide.