What this tool does
A BPDB prepaid meter never shows you kWh — you just recharge taka, and the meter prices your electricity as you use it. This tool reverses BPDB's official prepaid pricing to estimate how many units (kWh) each recharge funds and which month actually used them.
Step 1 — Turn each recharge into “energy money”
For a recharge of R taka, the meter peels off the non-energy charges first:
- VAT (5%) comes out of the whole recharge: VAT = R × 5 ÷ 105.
- Demand charge and meter rent are monthly — taken only on the first recharge of each calendar month. Demand charge = load(kW) × rate. If a month had no recharge at all, the next recharge pays that backlog (×N months).
- Rebate (1%) is added back: rebate = (R − VAT − meter rent) ÷ 101.
Energy money (E) = R − VAT − demand charge − meter rent + rebate
This energy money is not turned into a fixed number of units at the counter. BPDB's own example simply states the amount that “will be inserted in meter” — the meter holds it as a balance and prices kWh only as you consume.
Step 2 — Spread your use evenly across the days
A recharge isn't consumed the instant you buy it — it drains gradually until your next top-up. We assume you use roughly the same number of kWh each day across that window (not the same taka — cheap and expensive days cost differently). So a month's slice of the use is just its share of the days:
month's kWh = window's total kWh × (days of the window in that month ÷ total days in the window)
The window runs from each recharge up to (but not including) the next one, so no day is double-counted.
Step 3 — Price each day's use at its month's slab
BPDB rates are progressive: the first 75 units of a month are cheapest and each higher band costs more. The slab counter is cumulative within a calendar month and resets on the 1st — the meter prices each kWh by how much you have already consumed that month, not by when you recharged. So each day's use is billed up its month's slabs from that month's running total, and days that land in a fresh month start again at the cheap low bands.
How many kWh did the window actually buy? We pick the one total that makes the priced cost of all those days add up exactly to the energy money from Step 1. That's why a balance carrying into a new month buys more — its spillover days are billed at the reset, cheaper slabs — and why recharging early in a fresh month stretches further than topping up late in an expensive one.
Example. Suppose a recharge on 20 Jan works out to about 95 kWh of use and your next recharge was on 8 Feb. That's a 19-day window — 12 days fall in January (20–31 Jan) and 7 in February (1–7 Feb), and each month's slice is then priced at its own slab:
| Month | Days in window | Share | kWh credited |
|---|
| January | 12 | 12 / 19 | 60.0 |
| February | 7 | 7 / 19 | 35.0 |
Each month's total on the cards and chart is the sum of these slices from every recharge that overlaps it. A few finer points:
- Windows are half-open: the day of the next recharge starts the next window, so no day is counted twice and the slices always add back to the recharge's full kWh.
- The most recent recharge has no next top-up, so it's spread from its date up to today and marked pending — you likely haven't used it all yet, so it's excluded from the monthly averages.
- The first month in your data usually starts mid-month, so it captures only part of that month's use and can read low.
- This assumes roughly even daily use. Real consumption varies with weather and travel, so read each month as a solid estimate, not an exact meter figure.
Forecasting your next recharge
Your most recent top-up still has balance left in the meter. To estimate when it runs out, the tool takes your recent average daily use — kWh per day over roughly the last two months of completed windows — and drains the remaining energy money forward one day at a time, pricing each day at its month's slab and resetting on the 1st, until the balance reaches zero. That date is shown as Next recharge: the latest you'd need to top up if your usual habits hold. It shifts with weather and travel, so treat it as a heads-up, not a deadline.
Planning a recharge — the same maths, run backwards
The Plan a recharge panel answers the opposite question: if I want my next top-up to fall on a particular date, what do I recharge today? It assumes your current balance is about to run out, and works in two steps.
1. How much energy money the stretch needs. Exactly the forecast walk above, but summing instead of draining: step day by day from today to the day before your target, charge each day's kWh up its month's slabs — carrying on from the units you've already consumed this month, and resetting on the 1st — and add it all up. The balance therefore hits zero at the start of the target day, which is what makes that day the next recharge.
E = Σ (each day from today to target−1) cost of one day's kWh at that month's slab
2. Gross it back up into a recharge. Step 1 of the forward model turns a recharge R into energy money E. That formula inverts exactly — no guessing. With v = VAT rate and k = rebate ÷ (1 + rebate):
R = (1 + v) × [ (E + demand charge) ÷ (1 + k) + meter rent ]
The demand charge and meter rent are only in there if you haven't yet recharged this calendar month — top up again in a month you've already vended in and they drop out, so the whole recharge goes to energy. The result is rounded up to the nearest Tk 10.
One thing to watch. Those fixed charges are collected when you vend, not as you consume. So a recharge big enough to carry you past the end of the month doesn't pay next month's demand charge and rent — they pile up and are taken out of the next top-up. The panel warns you when that happens, and says how much is being deferred.
Leave the daily use box blank to plan at your recent average, or type a figure to plan around a heatwave or a trip away. Tick count the balance still left in the meter if you're topping up before the old balance is actually spent.
Slab rates used
Rates are set by BERC and applied automatically by date of use: the Feb 2024 schedule through 31 May 2026, and the Jun 2026 hike from 1 Jun 2026 onward.
Assumptions & limitations
- This is an estimate from recharge amounts and dates, not from meter readings.
- It assumes roughly even daily use between recharges.
- Demand charge defaults to 42 Tk/kW (a common bill figure); BPDB's published example uses 30 Tk/kW. Change it on the Tracker tab if yours differs.
- The Lifeline rate (≤ 50 kWh across a whole month) is not applied separately — it only matters for very low-usage months.
- The first month in your data is often partial, so its usage can read low.
Based on BPDB's official prepaid mechanics and worked example: bpdb.portal.gov.bd.