TryBuildCalcStandby Power Cost Calculator (Phantom / Vampire Power Cost)
Calculate your standby power cost.
🕒 Last updated: August 28, 2026
Inputs
Equipment
Pick a preset for a typical starting point, or choose Custom and enter your equipment's actual nameplate watts and usage pattern.
Equipment 1
ℹ️For equipment that draws a small amount of power even when off but still plugged in.
Equipment 2
ℹ️For equipment that draws a small amount of power even when off but still plugged in.
Equipment 3
ℹ️For equipment that draws a small amount of power even when off but still plugged in.
Electricity Rate
ℹ️Found on your utility bill — sometimes called the energy charge or price per unit (1 unit = 1 kWh).
ℹ️A fixed monthly fee your utility charges regardless of usage — include it for a full bill estimate, leave blank to see energy cost only.
Estimated Monthly Cost: $8.38
From 55.89 kWh/month at $0.1500/kWh
Cost by Period (Energy Only)
| Period | kWh | Cost |
|---|---|---|
| Day | 1.84 | $0.28 |
| Week | 12.85 | $1.93 |
| Month | 55.89 | $8.38 |
| Year | 670.70 | $100.61 |
Equipment Breakdown (Monthly)
| Equipment | kWh | Cost | Share |
|---|---|---|---|
| LED TV (40") (incl. standby) | 13.39 | $2.01 | 24.0% |
| Desktop Computer (incl. standby) | 27.89 | $4.18 | 49.9% |
| Custom (incl. standby) | 14.61 | $2.19 | 26.1% |
Assumptions Used
Month = 30.4375 days (365.25 ÷ 12) average, year = 365.25 days — avoids a lumpy figure tied to any one calendar month. Uses a flat electricity rate, not tiered or time-of-use pricing. This is a reference estimate — confirm against your actual utility bill and rate structure.
Planning backup power instead of running cost? UPS Battery Capacity Calculator →
Sizing a generator for this same equipment list instead? Generator Size Calculator →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Electricity Running Cost Calculator.
Standby / phantom power cost
Standby power is what electronics draw even when "off" but still plugged in — individually tiny, but it adds up across every always-plugged-in device in a home over a full year.
This page is pre-set with example standby watts for a TV and computer, plus a generic "always plugged in, never actively used" device (0 active hours, full-time standby) to show the pure phantom-load effect — edit to match your own devices.
- A device left plugged in but never turned on (0 hours/day active) still accrues standby cost around the clock.
- Chargers, game consoles, cable boxes, and appliances with a clock/display are common standby-power sources.
- Unplugging rarely-used devices, or using a switched power strip, eliminates their standby cost entirely.
Running Cost Formula: How Is It Calculated?
The core formula converts power (watts) and time (hours) into energy (kilowatt-hours), then applies your electricity rate.
Step 1 — Weekly Active Energy
Active kWh/week = (Watts × Quantity × Hours/Day × Days/Week) ÷ 1,000
This is the energy consumed while the equipment is actively running.
Step 2 — Weekly Standby Energy (Optional)
Standby Hours/Week = (24 × 7) − (Hours/Day × Days/Week)
Standby kWh/week = (Standby Watts × Quantity × Standby Hours/Week) ÷ 1,000
For equipment left plugged in, this adds the phantom-load energy consumed during all the hours it's not actively running.
Step 3 — Cost by Period
Weekly Cost = (Active kWh + Standby kWh) × Rate per kWh
Daily = Weekly ÷ 7, Monthly = Daily × 30.4375, Yearly = Daily × 365.25
Every equipment row's cost is summed together, and an optional monthly service charge is added on top to estimate a full bill.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Equipment | 3 items | Sets total energy consumption |
| Rate | $0.1500/kWh | Converts kWh to cost |
| Service Charge | None | Adds a fixed fee to the total bill estimate |
Step 1 — Weekly Energy per Equipment
Each row's active-hours energy is (Watts × Quantity × Hours/Day × Days/Week) ÷ 1,000. Any standby watts add energy for the remaining hours in the week (168 total).
| Equipment | Active Calculation | Standby Calculation | Weekly kWh |
|---|---|---|---|
| LED TV (40") | 100W × 1 × 4h × 7d ÷ 1000 = 2.80 kWh | 2W × 1 × 140.0h ÷ 1000 = 0.28 kWh | 3.08 |
| Desktop Computer | 200W × 1 × 6h × 5d ÷ 1000 = 6.00 kWh | 3W × 1 × 138.0h ÷ 1000 = 0.41 kWh | 6.41 |
| Custom | 5W × 4 × 0h × 0d ÷ 1000 = 0.00 kWh | 5W × 4 × 168.0h ÷ 1000 = 3.36 kWh | 3.36 |
Step 2 — Total Energy by Period
Every row's weekly kWh is summed, then converted: Daily = Weekly ÷ 7, Monthly = Daily × 30.4375, Yearly = Daily × 365.25.
| Period | Calculation | Total kWh |
|---|---|---|
| Week | 3.08 + 6.41 + 3.36 | 12.85 |
| Day | 12.85 ÷ 7 | 1.84 |
| Month | 1.84 × 30.4375 | 55.89 |
| Year | 1.84 × 365.25 | 670.70 |
Step 3 — Cost by Period
Each period's total kWh is multiplied by your electricity rate ($0.1500/kWh).
| Period | Calculation | Energy Cost |
|---|---|---|
| Day | 1.84 × $0.1500 | $0.28 |
| Month | 55.89 × $0.1500 | $8.38 |
| Year | 670.70 × $0.1500 | $100.61 |
Therefore, at $0.1500/kWh, your equipment costs approximately $8.38 per month ($100.61 per year) to run.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.