Methodology

OffPeakly uses published half-hourly import electricity rates for the selected Agile region.

Each day is divided into 48 half-hour slots. Prices are shown in pence per kWh and include VAT where the page labels them as inclusive. OffPeakly uses Europe/London time so slots match normal UK clock time, including daylight-saving changes.

Tomorrow’s prices are shown only once enough published data is available. Until then, OffPeakly marks tomorrow as pending or incomplete.

Agile prices vary by electricity region. OffPeakly lets you choose the relevant region and stores that preference in your browser.

The selected region affects current price, next price, cheapest remaining windows, appliance estimates, alerts, and comparison calculations.

If no region has been selected, OffPeakly uses a default region and keeps the active region visible.

The dashboard shows the active half-hour slot and the next half-hour slot based on the current time.

The current price helps with immediate checks. The next price matters when waiting a few minutes could change the result.

OffPeakly looks for useful blocks of time rather than only the single cheapest half-hour.

For a 1-hour window, it checks two consecutive half-hour slots. For a 2-hour window, it checks four consecutive slots. Appliance tools use the duration you select and find valid contiguous windows inside the chosen start and finish limits.

A window can be cheap but still unsuitable if it starts too late, ends after the selected finish time, overlaps a period you chose to avoid, is shorter than the appliance duration, or depends on tomorrow data that has not loaded.

The appliance timer estimates cost using:

estimated cost = appliance energy use × average unit rate across the selected run window

For presets, OffPeakly uses the duration and kWh assumptions shown in the UI. For custom appliances, it uses your chosen duration and power or energy input.

The timer compares valid windows and highlights the cheapest usable run. It can also show when running now is close enough to the best option that waiting is not worth much.

The estimate excludes standing charge, appliance start-up behaviour, changing power draw during the cycle, appliance-specific efficiency differences, and battery or charging losses unless those are explicitly modelled.

The late afternoon and early evening period is often the hardest part of Agile to use well. OffPeakly can flag or avoid the 4pm–7pm period for flexible loads.

This is not a rule for every household. It is a practical default because many expensive Agile periods appear around household demand peaks.

Alerts are region-specific and tied to the trigger you choose.

Alert types include tomorrow prices available, price below a chosen threshold, negative prices, and cheapest valid tomorrow window.

Email alerts require confirmation before activation. Each alert email includes an unsubscribe link.

The comparison tool gives an estimate, not a switching recommendation.

Quick estimate mode uses one total usage figure. Split mode uses timing assumptions such as overnight, daytime, and peak usage. A smart meter CSV summary can improve the estimate by showing when electricity is actually used.

Comparison results can change materially when usage lands in the evening peak, EV charging dominates the total, a battery shifts grid import, the selected region changes, standing charges differ, supplier eligibility rules apply, or tomorrow or historic prices are incomplete.

CSV files are processed locally in the browser. The raw file is not uploaded to OffPeakly.

The CSV is used to estimate average daily kWh, overnight usage share, daytime usage share, and peak-period usage share.

This is still only a summary. It does not replace a bill, supplier account data, or full tariff history.

When prices are missing, incomplete, or stale, OffPeakly shows that state clearly.

OffPeakly does not mark tomorrow as ready when only part of the day is available. When the data needed for a calculation is incomplete, the page uses a limited or pending state instead of a strong recommendation.

OffPeakly does not know your exact appliance model, whether someone is home, whether an appliance is already loaded, your supplier account status, your exact standing charge, every tariff eligibility rule, whether your smart meter readings are billing correctly, or whether a future price pattern will repeat.

Use the tools for planning and checking. Use your supplier’s tariff documents and bills for final decisions.