Tariff Calculator: When to Charge Your Phone, Laptop and Robot Vacuum

Worried your phone or robot vacuum is quietly inflating your energy bill? With tariffs fragmenting into flat, two-rate and dynamic offers in 2026, knowing exactly when to plug in can shave real cash off household bills. This interactive guide and built-in tariff calculator shows you the cheapest windows to charge phones, laptops, monitors and robot vacuums using your tariff and realistic device energy profiles — plus step-by-step scheduling actions you can implement today.

Quick answer: how the calculator helps you save

Use the tool below to enter your tariff (flat price, two-rate like Economy-style, or an hourly/dynamic price list), pick or enter a device profile and the run/charge time. The calculator will:

• Compute cost per charge and cost per hour or per day for continuous devices (like monitors).
• Search hourly rates to find the cheapest contiguous charge window for the device's required charging time.
• Suggest practical automation: smart plug schedules, charger settings and behavioural changes to reduce annual cost.

The context: why timing matters more in 2026

Energy retailing in late 2025 and early 2026 accelerated the shift away from one-size-fits-all flat tariffs. Suppliers now promote bespoke time-of-use (ToU) and dynamic deals that reflect wholesale volatility and growing solar/wind output. Meanwhile, smart meters and half-hourly settlement are mainstream enough that many households see hourly prices — so charge scheduling moved from novelty to necessity.

Key trends to keep in mind:

• More dynamic tariffs: Suppliers expanded dynamic offers after 2024–25 pilot programs. That means prices can vary by hour and sometimes be negative during high renewable generation.
• Daily price shapes changed: Midday troughs now appear in areas with lots of rooftop solar, while windy nights can still produce low overnight rates. The cheapest window isn’t always 2am anymore.
• Smart device automation: Cheap smart plugs and Matter-compatible hubs make precise charge scheduling easy and secure in 2026.

Interactive tariff calculator

Tip: pick a sample tariff or paste your own half-hourly/hourly prices in pence per kWh. Enter device data or choose a preset. The calculator will output the cheapest start time and the expected cost.

Understanding the math: cost per charge explained

There are two simple formulas you need.

1. Battery-based device (phone, laptop): energy (kWh) = battery_Wh / 1000 / efficiency (e.g., 15 Wh phone, 85% efficiency becomes ~0.018 kWh).
2. Continuous devices (monitor, vacuum while running): energy (kWh) = watts × hours / 1000 (e.g., 45 W monitor for 8 hours = 0.36 kWh).

Cost = energy (kWh) × price (p/kWh) / 100 to convert pence to pounds.

Real examples you can replicate

We use current 2026-style price shapes to show real savings.

Case study — phone charging cost (typical UK 2026 scenario)

Phone: 15 Wh battery, 85% charger efficiency → 0.0176 kWh per full charge. Under a flat 34 p/kWh tariff, cost per full charge = 0.0176 × 34p = 0.598p (~0.6p). Under a two-rate tariff with an 11 p overnight off-peak window, cost becomes 0.19p. If you charge 1 full cycle per day, switching the charge to the off-peak window saves about 1.5–2.4 GBP per year — small per device but large in aggregate when multiplied across household devices.

Case study — monitor energy use

Monitor: 32" gaming monitor at 60 W averaged across a day; daily usage 8 hours → 0.48 kWh/day. At 34 p/kWh that's £0.163/day, £59.50/year. Reducing brightness, enabling sleep after idle, and shifting usage where possible to low-price windows (or turning off overnight) can reduce this by 20–50% depending on behaviour and tariff.

Case study — robot vacuum schedule

Robot vacuum: typical energy per clean 0.05–0.12 kWh depending on runtime and suction level. Take 0.08 kWh per clean. At a 30 p/kWh average, cost per clean = 0.024p (virtually zero per clean); however, scheduling hundreds of cleans or using high-power mopping can change totals. If your supplier offers a deep off-peak like 8–12 p/kWh in a nightly window, scheduling the vacuum's recharge to that window (or using a timed smart-plug) adds up — savings of £5–£20/year for heavy users and pet households.

Actionable ways to implement charge scheduling

Here are practical steps, ordered by ease and impact.

1. Check if you have hourly data: If you have a smart meter and supplier portal or an app, download or copy hourly prices for a typical recent day into the calculator. If not, use your current flat price to estimate.
2. Measure before you change: Use a plug-in energy monitor (like the simple inline meters) or a smart plug with energy reporting. Measure one full charge/run to get real Wh consumption.
3. Pick the right automation:
   • Phones/laptops: use in-device timers or smart plugs set to start at the cheapest window.
   • Robot vacuums: most models have a “charge at” schedule; set it to resume charging during the identified cheapest window or control via a smart plug for older models.
   • Monitors: set sleep/eco modes and use a smart strip to cut power overnight or during peak price hours.
4. Use battery storage or EV chargers as aggregators: If you have a home battery or an EV, charge them in cheap windows and draw power locally when prices are high.
5. Review quarterly: Price shapes shift with seasons and renewable output; re-run calculations every 3 months (or let a smart energy app automate it).

Advanced strategies and predictions for 2026–2028

Looking ahead, the most financially savvy households will combine the following:

• Automated arbitrage: Homes with batteries will charge during negative or very low price midday windows (solar surplus) and power appliances later.
• Device-aware home energy management: New smart home hubs in 2025–26 understand the difference between battery charging and running loads and will schedule both for minimum system cost.
• Aggregator programs: Expect more supplier incentives to shift flexible demand (appliances, battery, EVs) into network-friendly windows — you could get credits for letting them adjust charging.

What that means for your small devices

Phones and laptops are low-energy but high-frequency. Scheduling their charges to the cheapest windows compounds an otherwise tiny per-charge saving into a meaningful annual reduction. For medium-to-high energy devices (robot vacuums running daily, monitors left on), automated scheduling and simple behavioural changes yield larger gains.

Common pitfalls and how to avoid them

• Assuming midnight is always cheapest: Check hourly patterns — in solar-heavy areas midday can be the cheapest.
• Ignoring standby losses: Devices left plugged in but idle consume small power; use smart strips for TVs/monitors where possible.
• Over-scheduling critical devices: If your robot vacuum must clean midday for pets/guests, don’t sacrifice convenience for marginal savings — use a hybrid schedule.

Equipment checklist

• Plug-in energy monitor or smart plug with energy reporting (Matter-compatible recommended in 2026)
• Smart plugs and smart strips for schedule automation
• Updated supplier app access or CSV of hourly prices (for dynamic tariffs)
• Battery storage or EV charging interface if available

Final checklist before you automate

• Measure one charge/run energy to replace assumptions with data.
• Confirm the cheapest contiguous window for the device’s required charge duration.
• Set a schedule in the device or smart plug and test for a week to confirm expected savings.
• Re-run the tariff calculator when seasons or tariff shapes change (or on plan renewal).

Wrap-up and call to action

Small devices individually cost pennies per charge, but the cumulative effect across phones, laptops, monitors and robot vacuums — multiplied over months — is meaningful. In 2026 the difference between a static mindset and a scheduled one is larger than ever, because tariffs now vary by hour and automation is cheap.

Ready to cut waste and schedule smarter? Use the interactive tariff calculator above, copy your hourly prices from your supplier app and run a quick measurement of your device. Then automate the cheapest window with a smart plug or native timer. If you want personalised help, our vetted installers and energy advisors can set up automation, measure device loads and recommend the most cost-effective tariffs for your home.

Try the calculator now — and save on electricity every month.

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