diff --git a/backend/src/lib/cost-calc.js b/backend/src/lib/cost-calc.js
index e2a5277..d367542 100644
--- a/backend/src/lib/cost-calc.js
+++ b/backend/src/lib/cost-calc.js
@@ -350,10 +350,17 @@ export async function getMeterEstimateForPeriod(meterId, periodStart, periodEnd,
   const today = toISODate(new Date())
   const asOfDate = today < periodEnd ? today : periodEnd
   const daysInPeriod = daysInclusive(periodStart, periodEnd)
-  const remainingDays = Math.max(daysBetween(asOfDate, periodEnd), 0)
 
   const { daily_rate } = await getTrailingDailyRate(meterId, windowDays)
-  const { consumption: actualToDate, has_data } = await getPeriodConsumption(meterId, periodStart, asOfDate)
+  const { consumption: actualToDate, has_data, last: lastReading } = await getPeriodConsumption(meterId, periodStart, asOfDate)
+
+  // Project from the meter's last actual reading, not from "today" — a meter
+  // read only every couple of weeks will almost always have its last reading
+  // sitting days before today, and projecting only from today would silently
+  // drop that gap from both the actual and projected totals.
+  const lastKnownDate = lastReading ? toISODate(lastReading.reading_date) : periodStart
+  const projectionFrom = lastKnownDate > periodStart ? lastKnownDate : periodStart
+  const remainingDays = Math.max(daysBetween(projectionFrom, periodEnd), 0)
 
   let projectedConsumption = null
   if (daily_rate != null) {