Does the energy price cap apply when you move in?

You are free to switch straight away, but there is a case for waiting briefly. The default tariff is capped and normally has no exit fee, so staying on it for one billing period costs you flexibility rather than locking you in. What you gain by waiting is a real usage figure for a property you have never lived in, which is what makes a fixed-tariff comparison meaningful. The risk of waiting is that the capped default is usually among the supplier's most expensive tariffs, so every month you stay is a month you may be overpaying. If you already know the property's annual kWh, compare now.

In almost every case, yes. Moving in without choosing a tariff places you on the existing supplier's default tariff. Ofgem describes the most common default as a deemed tariff that is standard variable, and the price cap covers standard variable tariffs. The exceptions are properties on heat networks, heating oil or LPG, supplies on a business contract, and situations where you do not hold the supply contract at all because energy is included in your rent.

No. The cap sets the maximum unit rate and standing charge a supplier may charge on a default tariff, not a fair or competitive one. Ofgem states that deemed contracts and default tariffs are usually among a supplier's most expensive. Being capped means you cannot be charged above a ceiling. It does not mean a cheaper tariff is unavailable, and frequently one is.

Normally not. Ofgem defines a standard variable tariff as a supply contract of indefinite length with no fixed term attached to its terms and conditions, and without a fixed term there is no early termination fee to charge. Confirm it with the supplier before switching, but the usual position is that you can leave a default tariff freely.

Your first bill can legitimately cover two rate periods, priced at the old rates up to the change date and the new rates from it. That is correct behaviour, not an error. What makes it accurate is a meter reading on the changeover date. Without one the supplier estimates the split, and an estimate that puts too much usage after the change date costs you money. Take a reading on the day the cap changes and send it in.

Not to the amount you pay. If you do not hold the supply contract, what you pay is set by your tenancy agreement rather than by Ofgem. Ofgem's maximum resale price rules stop a landlord charging more than they paid when they recharge energy separately, but those rules do not apply where energy is included in the rent. That means a bills-included rent or student package can sit above capped rates entirely lawfully, so the fair-usage limit in the agreement matters more to you than the cap does.

Ofgem publishes guidance on finding your current energy supplier, which covers the lookup services for electricity and gas separately. Do this before assuming which company to contact, because the previous occupant may have switched without the letting agent or seller knowing. Once you know the supplier, give them your move-in date and opening readings.

Waiting for one or two bills is reasonable if you do not know the property's usage, because dual fuel offers are worth comparing on total annual cost rather than on the discount attached to them. The cost of waiting is real though. You spend that period on a capped default that is usually one of the supplier's more expensive tariffs. Waiting for accuracy makes sense. Waiting indefinitely is just paying the default.

Ofgem's faster switching standard is up to five working days, and you can ask to be switched on a later date if that suits your move better. Practically, that means a decision made in the final week of a cap period can still complete before the next period begins.