Time-of-Use Electricity Cost & Peak Shaving Calculator

Time-of-Use Electricity Cost & Peak Shaving Calculator

Is a time-of-use tariff actually cheaper for you? Compares it against flat rate on your own usage pattern, then shows what moving one load into a cheaper window is worth over a year.

Your tariff

Filled in from your country as a starting point. Real tariffs differ between suppliers even in the same town, so put your own rates in if you have a bill to hand.

The expensive band, usually late afternoon to evening
/kWh
The middle band, if your tariff has one
/kWh
/kWh
The cheapest window, often for EV charging
/kWh
What you would pay on a single-rate tariff
/kWh
Advanced / Custom Input — the tariff
Charged on both tariffs, so it does not change the comparison — shown so the totals are real.
/day
Many tariffs charge the off-peak rate all weekend.
%
%
%

Your usage

From any recent bill
kWh
On a TOU tariff this matters far more than how much you use
Advanced / Custom Input — my own split
These four should add up to 100%. The tool normalises them if they do not.
%
%
%
%
days

A load you could move

The bigger and the more predictable, the better
kW
h
nos
Advanced / Custom Input — the shift
A dishwasher moves entirely. Air conditioning usually does not.
%
The tool works out how long it takes to pay for itself.

Thinking about a battery?

Leave at 0 to skip this part
kWh
Advanced / Custom Input — the battery
You lose some of every unit you store and take back out.
%
%
One a day is 365. Fewer if you only use it in one season.
nos

Result

Put in your rates and your usage, then press “Work out my bill”.

Estimate only — verify against your own tariff and your supplier’s current rates before switching.

Time-of-Use Tariff Calculator: TOU vs Flat Rate Savings

Most so called time of use tariff calculator tools online only ask how many kWh you used in a month, add them up and give you one number. That number can’t tell you anything useful, because on a TOU plan it’s not how much power you use that decides your bill, it’s when you use it. This tool is built differently, it compares a time-of-use tariff against your current flat rate using your own real usage split across peak, shoulder, off-peak and overnight bands, so it can honestly tell you to stay on flat rate if that’s actually cheaper for you. It also lets you simulate moving one load, like an EV charger or a dishwasher, into a cheaper band and checks whether a home battery’s peak shaving savings are enough to actually justify buying one. Made for homeowners, electricians and energy consultants comparing tariffs across the US, UK, Australia, Canada and several other countries.

How to Use

Step 1: Pick your region
  • At the top of the tool there’s a region dropdown. Select your country (USA, UK, Australia, Canada, Germany and 9 more are available). This fills in a realistic starting set of rates, a standing charge and the right currency symbol for that market automatically, you don’t have to go hunting for default numbers yourself.
Step 2: Type in your tariff’s actual rates
  • Enter the Peak rate, Shoulder rate, Off-peak rate and Overnight rate, all in cost-per-kWh, directly from your electricity bill or your utility’s published rate card. Then fill the “Your flat rate, for comparison” field with your current single rate tariff. This last field is what keeps the whole tool honest, without it there’s no real comparison, just a one-sided TOU pitch.
Step 3: Add your daily standing charge
  • Enter the fixed daily charge that appears on your bill regardless of usage. It gets added to both the TOU total and the flat total equally, so it never flips which tariff wins, but it has to be there for the final monthly figures to actually match what you’d really pay.
Step 4: Switch on weekend and seasonal rates if your tariff has them
  • If weekends are billed differently, toggle “Different rates at weekends?” to Yes and set what percentage of the weekday rate applies on Saturday and Sunday. If your peak rate goes up in summer and down in winter (or the other way), toggle “Summer and winter rates differ?” and set both percentages. Turning this on unlocks a month by month chart later, so a saving that only shows up in one season doesn’t get buried inside a single yearly average.
Step 5: Enter how much you use and roughly when
  • Type your average monthly kWh from a recent bill, then pick a usage profile from the dropdown, options like Daytime-heavy, Evening-heavy or Spread-out. This auto-fills four band share percentages for you (peak, shoulder, off-peak, night), and you can edit any of them directly if your smart meter app gives you your real split, which will always be more accurate than a preset.
Step 6: Set up the load you want to shift
  • Pick what you could realistically move, an EV charger, a dishwasher, a washing machine, a water heater, or a custom appliance, then fill in its power draw in kW, how long it runs each time, how many times a week, which band it currently runs in and which band you’d like to move it to. If only part of the load can actually move (say your AC can’t fully shift), lower the “shiftable share” percentage to reflect that.
Step 7: Add a battery only if you’re actually considering one
  • Enter a battery size in kWh and its rough cost. If you’re not thinking about a battery right now, just leave this at 0 and the tool skips this section entirely, no need to delete anything. In the advanced section you can fine tune round-trip efficiency, usable depth of discharge and how many cycles a year you expect to run it.
Step 8: Tap Calculate and read the result
  • The tool returns a clear verdict (TOU wins, stay on flat rate, or only worth it if you shift), your side by side monthly and yearly cost comparison, a table showing exactly where every rupee or dollar of your bill is going band by band, the real currency value of moving your chosen load and, if you entered a battery size, its yearly arbitrage earnings along with a simple payback period in years.

Key Features

  • Four separate rate bands, not just two. Most free calculators only do peak and off-peak. This one adds a shoulder (mid-peak) band and a dedicated overnight band too, because that’s how real tariffs like UK Economy 7 style plans and most Australian retailer plans are actually structured.
  • An honest flat-rate comparison, built in. The tool runs your exact same monthly kWh through a flat-rate calculation and places it right next to your TOU bill. If too much of your usage sits in the peak band, it will tell you straight that TOU costs more for you, it doesn’t just assume switching is always the better move.
  • Weekend rate blending that reflects a real week. When weekend rates are different, the engine blends the weekday and weekend rate using the real 5 day to 2 day split (5/7th weekday, 2/7th weekend) for every single band, so the number used in your final bill isn’t just a rough average guess.
  • A month by month seasonal chart. With seasonal rates turned on, the tool recalculates all twelve months separately, applying the seasonal multiplier only to the peak and shoulder bands since overnight pricing rarely moves much by season, then charts each month so you can actually see if winter wipes out a summer saving.
  • Load-shift value shown in your own currency. Give it any appliance’s power draw, run time and weekly frequency, pick where it runs from and where you’d move it to and the tool works out the real money value, power times hours times shiftable share times the rate difference between the two bands, multiplied by how often that happens across a year.
  • Battery arbitrage calculated after real losses. Instead of just showing you the theoretical gap between peak and overnight rates, the tool multiplies that spread by the round-trip efficiency you enter first, so what you see is what the battery genuinely earns per cycle, plus a payback period measured against its actual purchase cost.
  • Timer/smart-plug payback built in. If you add the cost of a smart plug or timer used to automate your load shift, the tool divides that cost by your yearly shifting saving and tells you in plain terms how many months it’ll take the device to pay for itself.

Formula / Logic Used

Effective rate per band (with optional weekend blending)

Re=R×57+R×Wp×27Re = R \times \frac{5}{7} + R \times Wp \times \frac{2}{7}

Monthly energy use per band

Ek=M×SkEk = M \times Sk

Monthly time-of-use bill

TOU=∑Ek×Rk+SC×DTOU = \sum Ek \times Rk + SC \times D

Monthly flat-rate bill (same units, for comparison)

Fl=M×Rf+SC×DFl = M \times Rf + SC \times D

Annual saving from switching to time-of-use

A=(Fl−TOU)×12A = (Fl – TOU) \times 12

Value of shifting one load between bands

Sv=Pk×H×Sh×(Rt−Rf)×N×52Sv = Pk \times H \times Sh \times (Rt – Rf) \times N \times 52

Battery arbitrage spread, after round-trip losses

Sp=(Rp−Rn)×ηSp = (Rp – Rn) \times \eta

Annual battery arbitrage value and simple payback

Av=B×U×Sp×CAv = B \times U \times Sp \times C

Pb=CbAvPb = \frac{Cb}{Av}

Who Should Use This Tool

Homeowners and renters trying to work out if switching to a time-of-use tariff genuinely saves them money, EV owners who want proof that overnight charging is actually worth the hassle and electrical engineers or energy consultants who need to model peak shaving savings and battery storage economics for clients across TOU markets like the US, UK and Australia.

Frequently Asked Questions (FAQs)

1. Is time-of-use electricity actually cheaper than a flat rate?

It depends completely on when you use power, not how much of it you use. If a big share of your usage falls in the peak band, a TOU tariff can end up costing more than flat rate and this calculator is built to tell you that honestly instead of pushing a switch no matter what.

2. How does an economy 7 calculator differ from a normal TOU calculator?

Economy 7 is a simple two-band UK tariff, day and night only, while this tool handles up to four bands (peak, shoulder, off-peak, overnight) plus weekend and seasonal variation, so Economy 7 is really just a simpler case inside a more flexible model here.

3. How much can I actually save by charging my EV overnight instead of during peak hours?

Multiply the charger’s kW by how many hours it runs, by the rate difference between your peak and overnight bands, then by how many times a week you charge. The load-shift section of this tool does exactly this and shows you the annual figure straight away.

4. Does a home battery really pay for itself on a time-of-use tariff?

Only if the peak-to-overnight rate spread, after round-trip efficiency losses, multiplied by usable battery capacity and your expected annual cycles, is bigger than what the battery cost you to buy, within a reasonable number of years. That’s exactly what the battery section here works out for you.

5. What’s the actual difference between peak shaving and load shifting?

Load shifting means moving one specific appliance’s run time into a cheaper rate band. Peak shaving is the broader idea, reducing or spreading out your overall peak-band demand, often using a battery or several scheduled devices together. This tool covers both, load shifting in the simulator and peak shaving through the battery arbitrage section.

Related Tools

  • Solar System Size & Payback Calculator – If you’re already looking at TOU rates, pairing solar with the right tariff can shift even more of your usage into the free or near-free daytime band, this tool sizes the system and works out the real payback.
  • EV Home Charger Load Compatibility Checker – Before you lock in an overnight charging schedule to chase off-peak rates, check here that your home’s panel and wiring can actually handle the charger safely.
  • Backup Generator Sizing Calculator – For homes where peak-hour grid reliability is also a concern alongside cost, this tool sizes a backup generator to cover your essential loads during an outage.
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