diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6aae237..7dca0ee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,6 +32,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Added
 
+- **`recommendations.Client.GetSPCommitmentRate`:** commitment dollars per
+  on-demand dollar (r) of the used part of a new Savings Plan, derived from CE
+  purchase recommendations as `(utilization/100) * EstimatedSPCost /
+  (EstimatedSPCost + EstimatedSavingsAmount)` (ratio of sums over matching
+  details). Strict raw-detail parsing; an absent field or no matching detail is
+  `ErrNoSPCommitmentRate`, never a 1:1 fallback. Nothing consumes it yet
+  (go#349, groundwork for converting on-demand ladder sizing to commitment
+  dollars).
+
 - **`recommendations.ApplyFamilyNUSizingRDSWithExpiryOptions`:** the
   rebuy-window RDS family sizing, plus credit for replacements already bought.
   Coverage is a lookback average, so RIs bought inside `CoverageLookbackDays`
diff --git a/providers/aws/recommendations/sp_commitment_rate.go b/providers/aws/recommendations/sp_commitment_rate.go
new file mode 100644
index 0000000..ba9784d
--- /dev/null
+++ b/providers/aws/recommendations/sp_commitment_rate.go
@@ -0,0 +1,188 @@
+package recommendations
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/service/costexplorer"
+	"github.com/aws/aws-sdk-go-v2/service/costexplorer/types"
+)
+
+// ErrNoSPCommitmentRate means Cost Explorer produced no usable Savings Plan
+// recommendation for the requested scope (no matching detail, a field the
+// formula needs is absent, or no covered on-demand spend). Callers must treat
+// the layer as having no rate (explainable Hold); they must never substitute a
+// 1:1 rate.
+var ErrNoSPCommitmentRate = errors.New("sp commitment rate: no usable recommendation detail")
+
+// SPCommitmentRateParams selects the recommendation details a rate is derived
+// from. All fields are required.
+type SPCommitmentRateParams struct {
+	// PlanType is COMPUTE_SP or EC2_INSTANCE_SP.
+	PlanType types.SupportedSavingsPlansType
+	// AccountID restricts details to this (linked) account.
+	AccountID string
+	// Region restricts details to this region. CE reports it on
+	// SavingsPlansDetails only for EC2 Instance SP; Compute SP details carry no
+	// region, so for COMPUTE_SP the result is the account-wide blend across
+	// EC2, Lambda and Fargate (an upper bound on the EC2 rate, see go#349 D6).
+	Region string
+	// Term is 1yr or 3yr; PaymentOption and LookbackPeriod use the same
+	// vocabulary as common.RecommendationParams.
+	Term           string
+	PaymentOption  string
+	LookbackPeriod string
+}
+
+// GetSPCommitmentRate returns r: commitment dollars per on-demand dollar for
+// the USED part of a new Savings Plan, derived from CE purchase
+// recommendations.
+//
+// EstimatedSavingsPercentage is measured against ALL applicable on-demand
+// spend, not just the covered part, so it cannot be used. Per detail:
+//
+//	covered_od = EstimatedSPCost + EstimatedSavingsAmount
+//	r          = (EstimatedAverageUtilization/100) * EstimatedSPCost / covered_od
+//
+// summed over the matching details (ratio of sums; every detail shares the
+// lookback so the hours cancel). The raw detail is parsed strictly: an absent
+// field is ErrNoSPCommitmentRate (never degraded to 0, which would give
+// r == utilization ~ 1:1), an unparseable or non-finite one is an error, and
+// a non-positive r (zero utilization) is an error; r <= 1 holds by construction
+// (non-negative savings, utilization <= 100).
+//
+// MANUAL VERIFICATION REQUIRED before relying on it with real money: the
+// semantics of the CE cost fields are verified only against the SDK docs and
+// a recorded fixture, not a live response.
+func (c *Client) GetSPCommitmentRate(ctx context.Context, p SPCommitmentRateParams) (float64, error) {
+	input, err := spRateInput(p)
+	if err != nil {
+		return 0, err
+	}
+	spCost, covered, matched, err := c.sumSPRateDetails(ctx, input, &p)
+	if err != nil {
+		return 0, err
+	}
+	if matched == 0 || covered <= 0 {
+		return 0, fmt.Errorf("%w: plan=%s region=%q term=%s payment=%s (%d matching details)",
+			ErrNoSPCommitmentRate, p.PlanType, p.Region, p.Term, p.PaymentOption, matched)
+	}
+	r := spCost / covered
+	if math.IsNaN(r) || r <= 0 {
+		return 0, fmt.Errorf("sp commitment rate: r=%g is not positive (used spend %g, covered on-demand %g)", r, spCost, covered)
+	}
+	return r, nil
+}
+
+// sumSPRateDetails pages through the recommendation and sums the used SP spend
+// and covered on-demand spend of every matching detail.
+func (c *Client) sumSPRateDetails(ctx context.Context, input *costexplorer.GetSavingsPlansPurchaseRecommendationInput, p *SPCommitmentRateParams) (spCost, covered float64, matched int, err error) {
+	for page := 0; ; page++ {
+		if page >= maxRecommendationPages {
+			return 0, 0, 0, fmt.Errorf("sp commitment rate: pagination cap reached after %d pages", maxRecommendationPages)
+		}
+		out, fetchErr := c.fetchSPPageWithRetry(ctx, input)
+		if fetchErr != nil {
+			return 0, 0, 0, fmt.Errorf("sp commitment rate: %w", fetchErr)
+		}
+		if out == nil {
+			break
+		}
+		if rec := out.SavingsPlansPurchaseRecommendation; rec != nil {
+			for i := range rec.SavingsPlansPurchaseRecommendationDetails {
+				d := &rec.SavingsPlansPurchaseRecommendationDetails[i]
+				if !spRateDetailMatches(d, p) {
+					continue
+				}
+				used, cov, err := spRateTerms(d)
+				if err != nil {
+					return 0, 0, 0, err
+				}
+				spCost += used
+				covered += cov
+				matched++
+			}
+		}
+		input.NextPageToken = out.NextPageToken
+		if aws.ToString(input.NextPageToken) == "" {
+			break
+		}
+	}
+	return spCost, covered, matched, nil
+}
+
+func spRateInput(p SPCommitmentRateParams) (*costexplorer.GetSavingsPlansPurchaseRecommendationInput, error) {
+	if p.PlanType != types.SupportedSavingsPlansTypeComputeSp && p.PlanType != types.SupportedSavingsPlansTypeEc2InstanceSp {
+		return nil, fmt.Errorf("sp commitment rate: unsupported plan type %q", p.PlanType)
+	}
+	if p.AccountID == "" || p.Region == "" {
+		return nil, errors.New("sp commitment rate: AccountID and Region are required")
+	}
+	payment, err := convertSavingsPlansPaymentOption(p.PaymentOption)
+	if err != nil {
+		return nil, fmt.Errorf("sp commitment rate: payment option: %w", err)
+	}
+	term, err := convertSavingsPlansTermInYears(p.Term)
+	if err != nil {
+		return nil, fmt.Errorf("sp commitment rate: term: %w", err)
+	}
+	lookback, err := convertSavingsPlansLookbackPeriod(p.LookbackPeriod)
+	if err != nil {
+		return nil, fmt.Errorf("sp commitment rate: lookback: %w", err)
+	}
+	return &costexplorer.GetSavingsPlansPurchaseRecommendationInput{
+		SavingsPlansType: p.PlanType, PaymentOption: payment, TermInYears: term,
+		LookbackPeriodInDays: lookback, AccountScope: types.AccountScopeLinked,
+	}, nil
+}
+
+// spRateDetailMatches filters details to the requested account and, for EC2
+// Instance SP, region.
+func spRateDetailMatches(d *types.SavingsPlansPurchaseRecommendationDetail, p *SPCommitmentRateParams) bool {
+	if aws.ToString(d.AccountId) != p.AccountID {
+		return false
+	}
+	if p.PlanType != types.SupportedSavingsPlansTypeEc2InstanceSp {
+		return true
+	}
+	return d.SavingsPlansDetails != nil &&
+		normalizeRegionName(aws.ToString(d.SavingsPlansDetails.Region)) == p.Region
+}
+
+// spRateTerms returns the used SP spend and the covered on-demand spend of one
+// detail, parsed strictly.
+func spRateTerms(d *types.SavingsPlansPurchaseRecommendationDetail) (usedSPCost, coveredOD float64, err error) {
+	spCost, err := spRateField("EstimatedSPCost", d.EstimatedSPCost)
+	if err != nil {
+		return 0, 0, err
+	}
+	savings, err := spRateField("EstimatedSavingsAmount", d.EstimatedSavingsAmount)
+	if err != nil {
+		return 0, 0, err
+	}
+	utilPct, err := spRateField("EstimatedAverageUtilization", d.EstimatedAverageUtilization)
+	if err != nil {
+		return 0, 0, err
+	}
+	if utilPct > 100 {
+		return 0, 0, fmt.Errorf("sp commitment rate: EstimatedAverageUtilization %g exceeds 100", utilPct)
+	}
+	return utilPct / 100 * spCost, spCost + savings, nil
+}
+
+// spRateField parses a required non-negative finite CE string field. Absent is
+// ErrNoSPCommitmentRate; present-but-invalid is a plain error.
+func spRateField(name string, v *string) (float64, error) {
+	if v == nil {
+		return 0, fmt.Errorf("%w: %s absent", ErrNoSPCommitmentRate, name)
+	}
+	f, err := strconv.ParseFloat(*v, 64)
+	if err != nil || math.IsNaN(f) || math.IsInf(f, 0) || f < 0 {
+		return 0, fmt.Errorf("sp commitment rate: %s %q is not a non-negative finite number", name, *v)
+	}
+	return f, nil
+}
diff --git a/providers/aws/recommendations/sp_commitment_rate_test.go b/providers/aws/recommendations/sp_commitment_rate_test.go
new file mode 100644
index 0000000..93ccfe0
--- /dev/null
+++ b/providers/aws/recommendations/sp_commitment_rate_test.go
@@ -0,0 +1,165 @@
+package recommendations
+
+import (
+	"context"
+	"errors"
+	"math"
+	"strconv"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/service/costexplorer"
+	"github.com/aws/aws-sdk-go-v2/service/costexplorer/types"
+)
+
+const lookback30dHours = 720.0
+
+// rateDetail builds a recorded-shape CE detail. All amounts are lookback
+// totals as CE returns them.
+func rateDetail(acct, region, spCost, savings, util string) types.SavingsPlansPurchaseRecommendationDetail {
+	d := types.SavingsPlansPurchaseRecommendationDetail{
+		AccountId:                   aws.String(acct),
+		EstimatedSPCost:             aws.String(spCost),
+		EstimatedSavingsAmount:      aws.String(savings),
+		EstimatedAverageUtilization: aws.String(util),
+		// Decoy: measured against ALL on-demand spend; must not drive r.
+		EstimatedSavingsPercentage: aws.String("18"),
+	}
+	if region != "" {
+		d.SavingsPlansDetails = &types.SavingsPlansDetails{Region: aws.String(region)}
+	}
+	return d
+}
+
+func rateClient(details ...types.SavingsPlansPurchaseRecommendationDetail) *Client {
+	return NewClientWithAPI(&mockCostExplorerAPI{
+		spRecommendations: &costexplorer.GetSavingsPlansPurchaseRecommendationOutput{
+			SavingsPlansPurchaseRecommendation: &types.SavingsPlansPurchaseRecommendation{
+				SavingsPlansPurchaseRecommendationDetails: details,
+			},
+		},
+	}, "us-east-1")
+}
+
+func rateParams(pt types.SupportedSavingsPlansType) SPCommitmentRateParams {
+	return SPCommitmentRateParams{PlanType: pt, AccountID: "acct-a", Region: "us-east-1",
+		Term: "1yr", PaymentOption: "no-upfront", LookbackPeriod: "30d"}
+}
+
+func TestGetSPCommitmentRate_FixtureCrossCheck(t *testing.T) {
+	// OD 1.00/hr over 720h = 720; CE says 300 stays on-demand with the SP, so
+	// covered_od = 420 = SPCost 294 + savings 126: r = 0.7 at full utilization.
+	// The 18% savings-vs-all-OD decoy would give 0.82 (the rejected formula).
+	currentOD := 1.0 * lookback30dHours
+	remainingOD := 300.0
+	d := rateDetail("acct-a", "US East (N. Virginia)", "294", "126", "100")
+	d.CurrentAverageHourlyOnDemandSpend = aws.String("1.0")
+	d.EstimatedOnDemandCost = aws.String(strconv.FormatFloat(remainingOD, 'f', -1, 64))
+	if got := currentOD - remainingOD; got != 420 {
+		t.Fatalf("fixture inconsistent: covered_od cross-check %g != 420", got)
+	}
+	r, err := rateClient(d).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if math.Abs(r-0.7) > 1e-12 {
+		t.Fatalf("r = %g, want 0.7", r)
+	}
+}
+
+func TestGetSPCommitmentRate_UtilizationScalesUsedSpend(t *testing.T) {
+	d := rateDetail("acct-a", "US East (N. Virginia)", "294", "126", "80")
+	r, err := rateClient(d).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+	if err != nil || math.Abs(r-0.56) > 1e-12 {
+		t.Fatalf("r = %g, err %v, want 0.56", r, err)
+	}
+}
+
+func TestGetSPCommitmentRate_RatioOfSumsNotMeanOfRatios(t *testing.T) {
+	// r1 = 0.5 (covered 20), r2 = 0.8 (covered 100): mean 0.65, ratio of sums
+	// (10+80)/120 = 0.75.
+	a := rateDetail("acct-a", "US East (N. Virginia)", "10", "10", "100")
+	b := rateDetail("acct-a", "US East (N. Virginia)", "80", "20", "100")
+	r, err := rateClient(a, b).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+	if err != nil || math.Abs(r-0.75) > 1e-12 {
+		t.Fatalf("r = %g, err %v, want 0.75", r, err)
+	}
+}
+
+func TestGetSPCommitmentRate_FiltersAccountAndRegion(t *testing.T) {
+	wrongAcct := rateDetail("acct-b", "US East (N. Virginia)", "10", "90", "100")
+	wrongRegion := rateDetail("acct-a", "EU (Ireland)", "10", "90", "100")
+	right := rateDetail("acct-a", "US East (N. Virginia)", "70", "30", "100")
+	r, err := rateClient(wrongAcct, wrongRegion, right).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+	if err != nil || math.Abs(r-0.7) > 1e-12 {
+		t.Fatalf("r = %g, err %v, want 0.7", r, err)
+	}
+}
+
+func TestGetSPCommitmentRate_ComputeSPIgnoresRegion(t *testing.T) {
+	d := rateDetail("acct-a", "", "60", "40", "100")
+	r, err := rateClient(d).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeComputeSp))
+	if err != nil || math.Abs(r-0.6) > 1e-12 {
+		t.Fatalf("r = %g, err %v, want 0.6", r, err)
+	}
+}
+
+func TestGetSPCommitmentRate_TypedAbsence(t *testing.T) {
+	missing := func(mut func(*types.SavingsPlansPurchaseRecommendationDetail)) types.SavingsPlansPurchaseRecommendationDetail {
+		d := rateDetail("acct-a", "US East (N. Virginia)", "70", "30", "100")
+		mut(&d)
+		return d
+	}
+	cases := map[string][]types.SavingsPlansPurchaseRecommendationDetail{
+		"no details":         nil,
+		"no matching detail": {rateDetail("acct-b", "US East (N. Virginia)", "70", "30", "100")},
+		"missing SP cost":    {missing(func(d *types.SavingsPlansPurchaseRecommendationDetail) { d.EstimatedSPCost = nil })},
+		"missing savings":    {missing(func(d *types.SavingsPlansPurchaseRecommendationDetail) { d.EstimatedSavingsAmount = nil })},
+		"missing util":       {missing(func(d *types.SavingsPlansPurchaseRecommendationDetail) { d.EstimatedAverageUtilization = nil })},
+		"zero covered":       {rateDetail("acct-a", "US East (N. Virginia)", "0", "0", "100")},
+	}
+	for name, details := range cases {
+		t.Run(name, func(t *testing.T) {
+			r, err := rateClient(details...).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+			if !errors.Is(err, ErrNoSPCommitmentRate) || r != 0 {
+				t.Fatalf("r = %g, err %v, want ErrNoSPCommitmentRate", r, err)
+			}
+		})
+	}
+}
+
+func TestGetSPCommitmentRate_InvalidFieldsAreErrors(t *testing.T) {
+	for name, d := range map[string]types.SavingsPlansPurchaseRecommendationDetail{
+		"unparseable": rateDetail("acct-a", "US East (N. Virginia)", "abc", "30", "100"),
+		"NaN":         rateDetail("acct-a", "US East (N. Virginia)", "NaN", "30", "100"),
+		"negative":    rateDetail("acct-a", "US East (N. Virginia)", "70", "-0.5", "100"),
+		"util > 100":  rateDetail("acct-a", "US East (N. Virginia)", "70", "30", "101"),
+	} {
+		t.Run(name, func(t *testing.T) {
+			_, err := rateClient(d).GetSPCommitmentRate(context.Background(), rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp))
+			if err == nil || errors.Is(err, ErrNoSPCommitmentRate) {
+				t.Fatalf("want a non-absence error, got %v", err)
+			}
+		})
+	}
+}
+
+func TestGetSPCommitmentRate_BadParams(t *testing.T) {
+	c := rateClient()
+	for name, mut := range map[string]func(*SPCommitmentRateParams){
+		"plan type": func(p *SPCommitmentRateParams) { p.PlanType = "SAGEMAKER_SP" },
+		"account":   func(p *SPCommitmentRateParams) { p.AccountID = "" },
+		"region":    func(p *SPCommitmentRateParams) { p.Region = "" },
+		"term":      func(p *SPCommitmentRateParams) { p.Term = "2yr" },
+		"payment":   func(p *SPCommitmentRateParams) { p.PaymentOption = "x" },
+		"lookback":  func(p *SPCommitmentRateParams) { p.LookbackPeriod = "9d" },
+	} {
+		t.Run(name, func(t *testing.T) {
+			p := rateParams(types.SupportedSavingsPlansTypeEc2InstanceSp)
+			mut(&p)
+			if _, err := c.GetSPCommitmentRate(context.Background(), p); err == nil {
+				t.Fatal("want error")
+			}
+		})
+	}
+}