Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

T. Rowe Price Index Trust, Inc.

Prospectus Date

rr_ProspectusDate

May 01, 2016

Supplement [Text Block]

trpiti_SupplementTextBlock

T. Rowe Price Equity Index 500 Fund

Supplement to Prospectus Dated May 1, 2016

The fund's Board of Directors has approved lowering the fund's expense limitation from 0.30% to 0.25%, effective September 1, 2016. On page 1, the fee table and expense example are revised as follows, effective September 1, 2016, to reflect the reduction of the expense limitation:

Fees and Expenses of the Fund

Shareholder fees (fees paid directly from your investment)
Maximum sales charge (load) imposed on purchases	NONE
Maximum deferred sales charge (load)	NONE
Redemption fee (as a percentage of amount redeemed on shares held for 90 days or less)	0.50%
Maximum account fee	$20a
Annual fund operating expenses (expenses that you pay each year as a percentage of the value of your investment)
Management fees	0.10%
Distribution and service (12b-1) fees	0.00%
Other expenses	0.17%
Total annual fund operating expenses	0.27%
Fee waiver/expense reimbursement	(0.02)%b,c
Total annual fund operating expenses after fee waiver/expense reimbursement	0.25%b,c

a Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.

b Restated to reflect current fees.

c T. Rowe Price Associates, Inc. has agreed (through April 30, 2019) to waive its fees and/or bear any expenses (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees) that would cause the fund's ratio of expenses to average daily net assets to exceed 0.25%. The agreement may be terminated at any time beyond April 30, 2019, with approval by the fund's Board of Directors. Fees waived and expenses paid under this agreement (and a previous limitation of 0.30%) are subject to reimbursement to T. Rowe Price Associates, Inc. by the fund whenever the fund's expense ratio is below 0.25%. However, no reimbursement will be made more than 3 years after the waiver or payment, or if it would result in the expense ratio exceeding 0.25% (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees).

Example This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, the fund’s operating expenses remain the same, and the expense limitation currently in place is not renewed. The figures have been adjusted to reflect fee waivers or expense reimbursements only in the periods for which the expense limitation arrangement is expected to continue. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 year	3 years	5 years	10 years
$26	$81	$146	$338

T. Rowe Price Equity Index 500 Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

trpiti_SupplementTextBlock

T. Rowe Price Equity Index 500 Fund

Supplement to Prospectus Dated May 1, 2016

The fund's Board of Directors has approved lowering the fund's expense limitation from 0.30% to 0.25%, effective September 1, 2016. On page 1, the fee table and expense example are revised as follows, effective September 1, 2016, to reflect the reduction of the expense limitation:

Fees and Expenses of the Fund

Shareholder fees (fees paid directly from your investment)
Maximum sales charge (load) imposed on purchases	NONE
Maximum deferred sales charge (load)	NONE
Redemption fee (as a percentage of amount redeemed on shares held for 90 days or less)	0.50%
Maximum account fee	$20a
Annual fund operating expenses (expenses that you pay each year as a percentage of the value of your investment)
Management fees	0.10%
Distribution and service (12b-1) fees	0.00%
Other expenses	0.17%
Total annual fund operating expenses	0.27%
Fee waiver/expense reimbursement	(0.02)%b,c
Total annual fund operating expenses after fee waiver/expense reimbursement	0.25%b,c

a Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.

b Restated to reflect current fees.

c T. Rowe Price Associates, Inc. has agreed (through April 30, 2019) to waive its fees and/or bear any expenses (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees) that would cause the fund's ratio of expenses to average daily net assets to exceed 0.25%. The agreement may be terminated at any time beyond April 30, 2019, with approval by the fund's Board of Directors. Fees waived and expenses paid under this agreement (and a previous limitation of 0.30%) are subject to reimbursement to T. Rowe Price Associates, Inc. by the fund whenever the fund's expense ratio is below 0.25%. However, no reimbursement will be made more than 3 years after the waiver or payment, or if it would result in the expense ratio exceeding 0.25% (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees).

Example This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, the fund’s operating expenses remain the same, and the expense limitation currently in place is not renewed. The figures have been adjusted to reflect fee waivers or expense reimbursements only in the periods for which the expense limitation arrangement is expected to continue. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1 year	3 years	5 years	10 years
$26	$81	$146	$338

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Fees and Expenses of the Fund

Shareholder fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual fund operating expenses
(expenses that you pay each year as a
percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2019

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Restated to reflect current fees.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, the fund’s operating expenses remain the same, and the expense limitation currently in place is not renewed. The figures have been adjusted to reflect fee waivers or expense reimbursements only in the periods for which the expense limitation arrangement is expected to continue. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

T. Rowe Price Equity Index 500 Fund | T. Rowe Price Equity Index 500 Fund

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load)

rr_MaximumDeferredSalesChargeOverOther

none

Redemption fee (as a percentage of amount redeemed on shares held for 90 days or less)

rr_RedemptionFeeOverRedemption

0.50%

Maximum account fee

rr_MaximumAccountFee

$ 20

^[1]

Management fees

rr_ManagementFeesOverAssets

0.10%

Distribution and service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.17%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.27%

Fee waiver/expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.02%)

^[2],[3]

Total annual fund operating expenses after fee waiver/expense reimbursement

rr_NetExpensesOverAssets

0.25%

^[2],[3]

1 year

rr_ExpenseExampleYear01

$ 26

3 years

rr_ExpenseExampleYear03

81

5 years

rr_ExpenseExampleYear05

146

10 years

rr_ExpenseExampleYear10

$ 338

[1] Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.

[2] Restated to reflect current fees.

[3] T. Rowe Price Associates, Inc. has agreed (through April 30, 2019) to waive its fees and/or bear any expenses (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees) that would cause the fund's ratio of expenses to average daily net assets to exceed 0.25%. The agreement may be terminated at any time beyond April 30, 2019, with approval by the fund's Board of Directors. Fees waived and expenses paid under this agreement (and a previous limitation of 0.30%) are subject to reimbursement to T. Rowe Price Associates, Inc. by the fund whenever the fund's expense ratio is below 0.25%. However, no reimbursement will be made more than 3 years after the waiver or payment, or if it would result in the expense ratio exceeding 0.25% (excluding interest, expenses related to borrowings, taxes and brokerage, extraordinary expenses, and acquired fund fees).