diff --git a/pkg/congestion/brutal.go b/pkg/congestion/brutal.go
index 95e7e59..81ae293 100644
--- a/pkg/congestion/brutal.go
+++ b/pkg/congestion/brutal.go
@@ -20,6 +20,7 @@ type BrutalSender struct {
 	pacer           *pacer
 
 	pktInfoSlots [pktInfoSlotCount]pktInfo
+	ackRate      float64
 }
 
 type pktInfo struct {
@@ -32,9 +33,10 @@ func NewBrutalSender(bps congestion.ByteCount) *BrutalSender {
 	bs := &BrutalSender{
 		bps:             bps,
 		maxDatagramSize: initMaxDatagramSize,
+		ackRate:         1,
 	}
-	bs.pacer = newPacer(func(now time.Time) congestion.ByteCount {
-		return congestion.ByteCount(float64(bs.bps) / bs.getAckRate(now))
+	bs.pacer = newPacer(func() congestion.ByteCount {
+		return congestion.ByteCount(float64(bs.bps) / bs.ackRate)
 	})
 	return bs
 }
@@ -60,7 +62,7 @@ func (b *BrutalSender) GetCongestionWindow() congestion.ByteCount {
 	if rtt <= 0 {
 		return 10240
 	}
-	return congestion.ByteCount(float64(b.bps) * rtt.Seconds() * 1.5 / b.getAckRate(time.Now()))
+	return congestion.ByteCount(float64(b.bps) * rtt.Seconds() * 1.5 / b.ackRate)
 }
 
 func (b *BrutalSender) OnPacketSent(sentTime time.Time, bytesInFlight congestion.ByteCount,
@@ -80,6 +82,7 @@ func (b *BrutalSender) OnPacketAcked(number congestion.PacketNumber, ackedBytes
 		b.pktInfoSlots[slot].AckCount = 1
 		b.pktInfoSlots[slot].LossCount = 0
 	}
+	b.updateAckRate(currentTimestamp)
 }
 
 func (b *BrutalSender) OnPacketLost(number congestion.PacketNumber, lostBytes congestion.ByteCount,
@@ -94,6 +97,7 @@ func (b *BrutalSender) OnPacketLost(number congestion.PacketNumber, lostBytes co
 		b.pktInfoSlots[slot].AckCount = 0
 		b.pktInfoSlots[slot].LossCount = 1
 	}
+	b.updateAckRate(currentTimestamp)
 }
 
 func (b *BrutalSender) SetMaxDatagramSize(size congestion.ByteCount) {
@@ -101,8 +105,7 @@ func (b *BrutalSender) SetMaxDatagramSize(size congestion.ByteCount) {
 	b.pacer.SetMaxDatagramSize(size)
 }
 
-func (b *BrutalSender) getAckRate(now time.Time) float64 {
-	currentTimestamp := now.Unix()
+func (b *BrutalSender) updateAckRate(currentTimestamp int64) {
 	minTimestamp := currentTimestamp - pktInfoSlotCount
 	var ackCount, lossCount uint64
 	for _, info := range b.pktInfoSlots {
@@ -113,13 +116,13 @@ func (b *BrutalSender) getAckRate(now time.Time) float64 {
 		lossCount += info.LossCount
 	}
 	if ackCount+lossCount < minSampleCount {
-		return 1
+		b.ackRate = 1
 	}
 	rate := float64(ackCount) / float64(ackCount+lossCount)
 	if rate < minAckRate {
-		return minAckRate
+		b.ackRate = minAckRate
 	}
-	return rate
+	b.ackRate = rate
 }
 
 func (b *BrutalSender) InSlowStart() bool {
diff --git a/pkg/congestion/pacer.go b/pkg/congestion/pacer.go
index 34bde7e..4370710 100644
--- a/pkg/congestion/pacer.go
+++ b/pkg/congestion/pacer.go
@@ -16,10 +16,10 @@ type pacer struct {
 	budgetAtLastSent congestion.ByteCount
 	maxDatagramSize  congestion.ByteCount
 	lastSentTime     time.Time
-	getBandwidth     func(time.Time) congestion.ByteCount // in bytes/s
+	getBandwidth     func() congestion.ByteCount // in bytes/s
 }
 
-func newPacer(getBandwidth func(time.Time) congestion.ByteCount) *pacer {
+func newPacer(getBandwidth func() congestion.ByteCount) *pacer {
 	p := &pacer{
 		budgetAtLastSent: maxBurstPackets * initMaxDatagramSize,
 		maxDatagramSize:  initMaxDatagramSize,
@@ -40,15 +40,15 @@ func (p *pacer) SentPacket(sendTime time.Time, size congestion.ByteCount) {
 
 func (p *pacer) Budget(now time.Time) congestion.ByteCount {
 	if p.lastSentTime.IsZero() {
-		return p.maxBurstSize(now)
+		return p.maxBurstSize()
 	}
-	budget := p.budgetAtLastSent + (p.getBandwidth(now)*congestion.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
-	return minByteCount(p.maxBurstSize(now), budget)
+	budget := p.budgetAtLastSent + (p.getBandwidth()*congestion.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
+	return minByteCount(p.maxBurstSize(), budget)
 }
 
-func (p *pacer) maxBurstSize(now time.Time) congestion.ByteCount {
+func (p *pacer) maxBurstSize() congestion.ByteCount {
 	return maxByteCount(
-		congestion.ByteCount((minPacingDelay+time.Millisecond).Nanoseconds())*p.getBandwidth(now)/1e9,
+		congestion.ByteCount((minPacingDelay+time.Millisecond).Nanoseconds())*p.getBandwidth()/1e9,
 		maxBurstPackets*p.maxDatagramSize,
 	)
 }
@@ -62,7 +62,7 @@ func (p *pacer) TimeUntilSend() time.Time {
 	return p.lastSentTime.Add(maxDuration(
 		minPacingDelay,
 		time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/
-			float64(p.getBandwidth(time.Now()))))*time.Nanosecond,
+			float64(p.getBandwidth())))*time.Nanosecond,
 	))
 }