Rates quoted are the PUCSL-approved Time-of-Use domestic tariff effective 11 May 2026 — the same numbers the calculator uses. TOU is optional and currently offered on a trial basis.
What TOU Metering Is
A normal meter counts total units. A TOU meter records when you used them, splitting your consumption into three windows — each billed at a different rate:
| Window | 12-hour | Official window | Rate (Rs./kWh) |
|---|---|---|---|
| Peak | 6:30 PM – 10:30 PM | 18:30 – 22:30 | 106.00 |
| Day | 5:30 AM – 6:30 PM | 05:30 – 18:30 | 47.00 |
| Off-peak | 10:30 PM – 5:30 AM | 22:30 – 05:30 | 33.00 |
Fixed charge: Rs. 2,500/month on top of the energy charges, plus the 2.5% SSCL — the same gross-up as the flat tariff.
The trade is simple: expensive evenings, cheap nights.
Who Qualifies
Per the published CEB terms, the domestic TOU tariff is offered to:
- Domestic consumers with a 3-phase, 30A (or higher) supply — most single-phase homes do not qualify
- Customers who voluntarily opt in — nobody is moved onto TOU automatically
- LECO customers can apply through LECO for their equivalent TOU option
If your home is single-phase, upgrading to 3-phase is a separate (paid) service-connection change — factor that cost in before chasing TOU savings.
How to Apply
- Check your connection — look at your bill or meter panel for a 3-phase/30A+ supply, or ask your provider.
- Visit your nearest CEB Area Office (or LECO office for LECO supply areas) and request the Time-of-Use tariff for domestic consumers.
- Meter replacement — the provider installs a TOU-capable meter that logs peak/day/off-peak units separately.
- Track the first bill — confirm the bill now shows three unit rows instead of one. If your peak-window usage was underestimated, the first bill will tell you honestly.
The Honest Break-Even Math
TOU is not automatically cheaper. Below roughly 250–300 units (the exact line depends on your split — see the table below) the flat tariff wins, because the Rs. 2,500 fixed charge plus peak pricing eat the off-peak discount. Computed with whole-bill math (slabs + fixed charge + 2.5% SSCL):
| Monthly units | Flat tariff bill | TOU bill (30% peak / 40% day / 30% night) | Winner |
|---|---|---|---|
| 150 kWh | Rs. 5,231 | ~Rs. 11,872 | Flat — by a mile |
| 200 kWh | Rs. 10,615 | ~Rs. 14,974 | Flat |
| 300 kWh | Rs. 20,872 | ~Rs. 21,179 | Flat — barely (~Rs. 300) |
| 350 kWh | Rs. 26,000 | ~Rs. 24,282 | TOU — ~Rs. 1,718/mo |
| 400 kWh | Rs. 31,128 | ~Rs. 27,385 | TOU — ~Rs. 3,743/mo |
| 500 kWh | Rs. 41,385 | ~Rs. 33,590 | TOU — ~Rs. 7,795/mo |
Now the dangerous part — a peak-heavy split makes TOU worse at any size. If half your units land in the 6:30–10:30 PM peak window (50% peak / 30% day / 20% night), 400 units costs Rs. 32,800 on TOU vs Rs. 31,128 flat — you pay more.
The crossover depends on the whole split, not just nights. Whole-bill math (slabs + Rs. 2,500 TOU fixed charge + 2.5% SSCL):
| Peak / day / night split | TOU beats flat above roughly |
|---|---|
| 20% / 30% / 50% | ~253 units |
| 25% / 35% / 40% | ~278 units |
| 30% / 30% / 40% | ~298 units |
| 30% / 40% / 30% | ~308 units |
| 40% / 40% / 20% | ~378 units |
| 50% / 30% / 20% | ~462 units |
| 50% / 50% / 0% — nothing at night | ~518 units |
Two myths to drop: nights are not the whole game (the daytime band at Rs. 47/kWh already beats the flat rate at high usage — 400 units run entirely in the day window bills ~Rs. 21,846), and peak share is the real enemy (at 60% peak / 40% day the crossover pushes to ~691 units).
What to Actually Shift
The whole game is moving big loads into the off-peak window:
- EV / vehicle charging — the single biggest win; overnight charging is what TOU is made for
- Water heaters / hot water — timer to 5:00 AM or evening after 10:30 PM
- Washing machine + dryer — schedule overnight cycles
- AC compressors pre-cooling — cool the room before 6:30 PM, coast through peak
- Pool pumps, borehole pumps — timer-controlled, run at night
Peak-window habits to break: cooking on electric appliances 6:30–10:30 PM, evening AC clusters, evening laundry.
Should You Switch?
Switch if: you use 350+ units/month, have a 3-phase connection, and can genuinely move hot water, laundry, or charging overnight.
Don't switch if: you're under ~300 units, single-phase, or your household is busiest exactly at 6:30–10:30 PM (cooking + AC + entertainment at once).
Try your own numbers first — the CEB & LECO Bill Calculator has a "Calculate with time-of-use rates" toggle that splits your units into the three windows and shows both bills side by side.
Frequently Asked Questions
Is TOU metering compulsory? No. It is a voluntary tariff offered on a trial basis since 2015 — you opt in, and you apply to switch back out if it doesn't suit you.
What are the off-peak hours in Sri Lanka? 10:30 PM to 5:30 AM (22:30–05:30) — overnight. The daytime window 5:30 AM–6:30 PM is the mid-priced "Day" band, not the cheapest.
Does TOU work with solar? Solar exports and TOU metering are separate arrangements — TOU governs what you import; check with CEB/LECO how TOU interacts with your net-metering or Net Plus scheme before switching.
What's the catch? The Rs. 2,500/month fixed charge and the Rs. 106/kWh peak rate. If life happens in the evenings, TOU costs more than the flat tariff — the math above shows exactly where the line is.
Rates verified against the PUCSL-approved tariff revision effective 11 May 2026. Application terms (3-phase 30A+, area-office process) per CEB's published TOU tariff page; confirm current terms with your provider before applying.