diff --git a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/GenotypingEngine.java b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/GenotypingEngine.java
index 2439e6219..b144170a7 100644
--- a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/GenotypingEngine.java
+++ b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/GenotypingEngine.java
@@ -504,7 +504,7 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
      * @return never {@code null}, an array with exactly <code>total-ploidy(vc) + 1</code> positions.
      */
     protected final double[] getAlleleFrequencyPriors( final VariantContext vc, final int defaultPloidy, final GenotypeLikelihoodsCalculationModel.Model model ) {
-        final int totalPloidy = GATKVariantContextUtils.totalPloidy(vc,defaultPloidy);
+        final int totalPloidy = GATKVariantContextUtils.totalPloidy(vc, defaultPloidy);
         switch (model) {
             case SNP:
             case GENERALPLOIDYSNP:
@@ -668,4 +668,50 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
         return MLEfrequencies;
     }
 
+    /**
+     * Calculates the active state profile value for a single sample.
+     *
+     * @param log10GenotypeLikelihoods the single sample genotype likelihoods.
+     * @return log10 probability from 0 to -Infinity.
+     */
+    public double calculateSingleSampleRefVsAnyActiveStateProfileValue(final double[] log10GenotypeLikelihoods) {
+        if (log10GenotypeLikelihoods == null) {
+            throw new IllegalArgumentException("the input likelihoods cannot be null");
+        } else if (log10GenotypeLikelihoods.length != this.configuration.genotypeArgs.samplePloidy + 1) {
+            throw new IllegalArgumentException("wrong likelihoods dimensions");
+        } else {
+            final double[] log10Priors = log10AlleleFrequencyPriorsSNPs.forTotalPloidy(this.configuration.genotypeArgs.samplePloidy);
+            final double log10ACeq0Likelihood = log10GenotypeLikelihoods[0];
+            final double log10ACeq0Prior = log10Priors[0];
+            final double log10ACeq0Posterior = log10ACeq0Likelihood + log10ACeq0Prior;
+
+            // If the Maximum a-posteriori AC is 0 then the profile value must be 0.0 as per existing code; it does
+            // not matter whether a AC > 0 is at all plausible.
+            boolean mapACeq0 = true;
+            for (int AC = 1; AC < log10Priors.length; AC++)
+                if (log10Priors[AC] + log10GenotypeLikelihoods[AC] > log10ACeq0Posterior) {
+                    mapACeq0 = false;
+                    break;
+                }
+            if (mapACeq0)
+                return 0.0;
+
+            //TODO bad way to calculate AC > 0 posterior that follows the current behaviour of ExactAFCalculator (StateTracker)
+            //TODO this is the lousy part... this code just adds up lks and priors of AC != 0 before as if
+            //TODO Sum(a_i * b_i) is equivalent to Sum(a_i) * Sum(b_i)
+            //TODO This has to be changed not just here but also in the AFCalculators (StateTracker).
+            final double log10ACgt0Likelihood = MathUtils.approximateLog10SumLog10(log10GenotypeLikelihoods, 1, log10GenotypeLikelihoods.length);
+            final double log10ACgt0Prior = MathUtils.approximateLog10SumLog10(log10Priors, 1, log10Priors.length);
+            final double log10ACgt0Posterior = log10ACgt0Likelihood + log10ACgt0Prior;
+            final double log10PosteriorNormalizationConstant = MathUtils.approximateLog10SumLog10(log10ACeq0Posterior, log10ACgt0Posterior);
+            //TODO End of lousy part.
+
+            final double normalizedLog10ACeq0Posterior = log10ACeq0Posterior - log10PosteriorNormalizationConstant;
+            // This is another condition to return a 0.0 also present in AFCalculator code as well.
+            if (normalizedLog10ACeq0Posterior >= QualityUtils.qualToErrorProbLog10(configuration.genotypeArgs.STANDARD_CONFIDENCE_FOR_EMITTING))
+                return 0.0;
+
+            return 1.0 - Math.pow(10.0, normalizedLog10ACeq0Posterior);
+        }
+    }
 }
diff --git a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/afcalc/StateTracker.java b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/afcalc/StateTracker.java
index ec858270b..9347ad2b5 100644
--- a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/afcalc/StateTracker.java
+++ b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/genotyper/afcalc/StateTracker.java
@@ -222,6 +222,7 @@ final class StateTracker {
     @Requires("allelesUsedInGenotyping != null")
     protected AFCalculationResult toAFCalculationResult(final double[] log10PriorsByAC) {
         final int [] subACOfMLE = Arrays.copyOf(alleleCountsOfMLE, allelesUsedInGenotyping.size() - 1);
+        //TODO bad calculation of normalized log10 ACeq0 and ACgt0 likelihoods, priors and consequently posteriors calculated in AFCalculationResult constructor.
         final double[] log10Likelihoods = MathUtils.normalizeFromLog10(new double[]{getLog10LikelihoodOfAFzero(), getLog10LikelihoodOfAFNotZero()}, true);
         final double[] log10Priors = MathUtils.normalizeFromLog10(new double[]{log10PriorsByAC[0], MathUtils.log10sumLog10(log10PriorsByAC, 1)}, true);
 
diff --git a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/haplotypecaller/HaplotypeCaller.java b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/haplotypecaller/HaplotypeCaller.java
index 7d41f37df..242e5b867 100644
--- a/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/haplotypecaller/HaplotypeCaller.java
+++ b/protected/gatk-tools-protected/src/main/java/org/broadinstitute/gatk/tools/walkers/haplotypecaller/HaplotypeCaller.java
@@ -811,9 +811,16 @@ public class HaplotypeCaller extends ActiveRegionWalker<List<VariantContext>, In
         }
 
         final List<Allele> alleles = Arrays.asList(FAKE_REF_ALLELE , FAKE_ALT_ALLELE);
-        final VariantCallContext vcOut = activeRegionEvaluationGenotyperEngine.calculateGenotypes(new VariantContextBuilder("HCisActive!", context.getContig(), context.getLocation().getStart(), context.getLocation().getStop(), alleles).genotypes(genotypes).make(), GenotypeLikelihoodsCalculationModel.Model.SNP);
-        final double isActiveProb = vcOut == null ? 0.0 : QualityUtils.qualToProb( vcOut.getPhredScaledQual() );
+        final double isActiveProb;
 
+        if (genotypes.size() == 1) {
+            // Faster implementation avoiding the costly and over complicated Exact AFCalculator machinery:
+            // This is the case when doing GVCF output.
+            isActiveProb = activeRegionEvaluationGenotyperEngine.calculateSingleSampleRefVsAnyActiveStateProfileValue(genotypes.get(0).getLikelihoods().getAsVector());
+        } else {
+            final VariantCallContext vcOut = activeRegionEvaluationGenotyperEngine.calculateGenotypes(new VariantContextBuilder("HCisActive!", context.getContig(), context.getLocation().getStart(), context.getLocation().getStop(), alleles).genotypes(genotypes).make(), GenotypeLikelihoodsCalculationModel.Model.SNP);
+            isActiveProb = vcOut == null ? 0.0 : QualityUtils.qualToProb(vcOut.getPhredScaledQual());
+        }
         return new ActivityProfileState( ref.getLocus(), isActiveProb, averageHQSoftClips.mean() > AVERAGE_HQ_SOFTCLIPS_HQ_BASES_THRESHOLD ? ActivityProfileState.Type.HIGH_QUALITY_SOFT_CLIPS : ActivityProfileState.Type.NONE, averageHQSoftClips.mean() );
     }