FairWatt: Accurate EV Charging & Utility Bill Splitting

Quick Intro

Welcome to the clean energy corner of the internet where we stop guessing how much your electric car actually costs to plug in at home! If you’ve made it here, you’re likely an EV owner trying to figure out your exact power footprint, or you’re in the high-stakes world of roommate utility management.

Side Note: Wait, why not just look at the utility bill?

Great question! Because your utility bill gives you one giant, terrifying total number for the whole house. It doesn't break down how much power went into your EV vs. your roommate's gaming rig or the AC. FairWatt bridges that gap by calculating exact charging session costs—accounting for wall-to-battery efficiency losses—so nobody pays a penny more or less than their fair share.

I’m your host—an EV driver who got tired of back-of-the-napkin napkin math, wall-loss estimates, and awkward monthly "who owes what" texts. FairWatt was built to turn kitchen-table utility math into a 10-second task. No subscriptions, no telemetry hardware to install, no accounts to set up, and zero data tracking. Just quick, accurate numbers.

How It Works (The Math)

Gather 'round, fellow energy nerds! Let’s talk about wall-to-battery conversion efficiency—the hidden factor most simple calculators ignore.

When you plug your EV into a 120V (Level 1) or 240V (Level 2) outlet, not every kilowatt-hour (kWh) drawn from the wall makes it directly into your battery. Some energy is lost as heat, onboard AC-to-DC conversion, and battery thermal management. 

- Level 1 Charging (120V): Typically operates around 75%–85% efficiency.

- Level 2 Charging (240V): Typically operates around 85%–92% efficiency.

FairWatt accounts for this efficiency factor automatically. When you input your starting and ending battery percentages, FairWatt calculates the true kWh drawn from the utility grid, ensuring your dollar calculations reflect what you're actually billed by your power company.

(Side Note Again: You can easily adjust your custom Efficiency Factor and Utility Rates in the app's Settings menu to match your exact home setup!)

Frequently Asked Questions

1. How do I split bills fairly with roommates?

Enter your household's total utility bill into FairWatt along with your logged EV charging sessions for that billing cycle. FairWatt isolates the total dollar amount spent strictly on EV charging, subtracts it from the master bill, and evenly splits the remaining baseline household utility balance among all roommates.

2. What rate should I enter for Off-Peak vs. Peak?

Check your monthly electric bill or utility portal. If your utility uses Time-of-Use (TOU) pricing, enter your Off-Peak rate (e.g., $0.12/kWh) and Peak rate (e.g., $0.35/kWh). If you have a flat rate, simply enter the same rate in both fields.

3. Does FairWatt connect directly to my car or charger?

No! FairWatt is intentionally independent and privacy-focused. You don't need to hand over your Tesla, Rivian, or utility account credentials. Simply log your start/target battery percentages, and FairWatt does the heavy lifting locally on your device.

What I've Learned

After tracking EV charging costs across different seasons and charge levels, one thing is clear: small efficiency losses and tier rates add up quickly over a full year. 

Whether you're trying to track your personal return on investment vs. gas, or just trying to keep housemate harmony intact when the summer power bill arrives, clarity is everything. 

Privacy Policy

Effective Date: August 30, 2026

The Short Version (TL;DR)

FairWatt doesn't track you, sell your data, collect your personal information, or transmit your charging history to shadowy third-party brokers. In fact, we don’t even have a server to send it to. Everything you put into FairWatt stays on your device. Period.

1. Information We Collect (Spoiler: None)

FairWatt was built with privacy as a core feature, not an afterthought. 

• No Accounts Required: You don't need to sign up, log in, or hand over an email address to use the app.

• No Vehicle Telemetry Access: FairWatt never asks for your Tesla, Rivian, or utility company login credentials.

• No Tracking or Analytics: We do not track your location, your charging locations, your app usage habits, or your hardware identifiers.

• No Cookies: This support site doesn't place tracking cookies on your device.

2. Local Data Storage

Any numbers you punch into the app—like your battery capacity, utility rates, charging sessions, and roommate split preferences—are stored locally on your iPhone. 

If you delete the FairWatt app from your device, your saved data and settings are deleted along with it. We cannot restore your data for you because we never had access to it in the first place.

3. Third-Party Services & Payment Processing

• App Store Processing: Payments, downloads, and app updates are handled entirely by Apple through the App Store. Apple handles your payment info according to their own privacy policy. FairWatt never sees your credit card or financial details.

• External Links: This website may contain links to external resources (like utility rate guides or Apple’s App Store). We aren't responsible for the privacy practices of those external sites, though we try to only link to reputable places.

4. Contact & Support

If you send an email to our support line (cot.soppy.0m@icloud.com), we will only use your email address to reply to your question or bug report. We won't add you to a marketing newsletter, sell your email to spammers, or bother you once your issue is sorted out.

5. Changes to This Policy

If we ever add optional features down the road that require cloud sync, we will update this policy clearly before you update your app. But for now, sit back, calculate your bill splits, and enjoy complete privacy.

Get the App!

Ready to take complete control of your EV charging expenses? 

FairWatt is available on the App Store for iPhone: https://apps.apple.com/us/app/fairwatt/id6806872127

Got questions, need help setting up your utility rates, or want to suggest a new feature? Drop me an email anytime at: cot.soppy.0m@icloud.com. (And yes, that’s a real address—thanks to Apple's "Hide My Email," I’ve got a handle that sounds like a minor laundry room catastrophe, but it lands straight in my inbox!)