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Secured and unsecured senior debt
 9 Months Ended
Sep. 30, 2025
Debt Disclosure [Abstract]  
Secured and unsecured senior debt SECURED AND UNSECURED SENIOR DEBTThe following table summarizes our outstanding indebtedness and respective principal payments remaining as of September 30, 2025 (dollars in thousands):
Stated 
Rate
Interest
Rate(1)
Maturity
Date(2)
Principal Payments Remaining for the Periods Ending December 31,
Unamortized
(Deferred
Financing
Cost),
(Discount)/
Premium
Debt
2025
2026
2027
2028
2029
Thereafter
Principal
Total
Unsecured senior line of credit and
commercial paper program(3)
(3)
4.52%
(3)
1/22/30
(3)
$—
$—
$—
$—
$—
$1,550,000
$1,550,000
$(1,458)
$1,548,542
Unsecured senior notes payable
4.30%
4.50
1/15/26
—
300,000
—
—
—
—
300,000
(160)
299,840
Unsecured senior notes payable
3.80%
3.96
4/15/26
—
350,000
—
—
—
—
350,000
(285)
349,715
Unsecured senior notes payable
3.95%
4.13
1/15/27
—
—
350,000
—
—
—
350,000
(684)
349,316
Unsecured senior notes payable
3.95%
4.07
1/15/28
—
—
—
425,000
—
—
425,000
(994)
424,006
Unsecured senior notes payable
4.50%
4.60
7/30/29
—
—
—
—
300,000
—
300,000
(860)
299,140
Unsecured senior notes payable
2.75%
2.87
12/15/29
—
—
—
—
400,000
—
400,000
(1,757)
398,243
Unsecured senior notes payable
4.70%
4.81
7/1/30
—
—
—
—
—
450,000
450,000
(1,779)
448,221
Unsecured senior notes payable
4.90%
5.05
12/15/30
—
—
—
—
—
700,000
700,000
(4,143)
695,857
Unsecured senior notes payable
3.375%
3.48
8/15/31
—
—
—
—
—
750,000
750,000
(3,866)
746,134
Unsecured senior notes payable
2.00%
2.12
5/18/32
—
—
—
—
—
900,000
900,000
(6,275)
893,725
Unsecured senior notes payable
1.875%
1.97
2/1/33
—
—
—
—
—
1,000,000
1,000,000
(6,458)
993,542
Unsecured senior notes payable
2.95%
3.07
3/15/34
—
—
—
—
—
800,000
800,000
(6,668)
793,332
Unsecured senior notes payable
4.75%
4.88
4/15/35
—
—
—
—
—
500,000
500,000
(4,615)
495,385
Unsecured senior notes payable
5.50%
5.66
10/1/35
—
—
—
—
—
550,000
550,000
(6,470)
543,530
Unsecured senior notes payable
5.25%
5.38
5/15/36
—
—
—
—
—
400,000
400,000
(3,853)
396,147
Unsecured senior notes payable
4.85%
4.93
4/15/49
—
—
—
—
—
300,000
300,000
(2,785)
297,215
Unsecured senior notes payable
4.00%
3.91
2/1/50
—
—
—
—
—
700,000
700,000
9,880
709,880
Unsecured senior notes payable
3.00%
3.08
5/18/51
—
—
—
—
—
850,000
850,000
(10,938)
839,062
Unsecured senior notes payable
3.55%
3.63
3/15/52
—
—
—
—
—
1,000,000
1,000,000
(13,339)
986,661
Unsecured senior notes payable
5.15%
5.26
4/15/53
—
—
—
—
—
500,000
500,000
(7,427)
492,573
Unsecured senior notes payable
5.625%
5.71
5/15/54
—
—
—
—
—
600,000
600,000
(6,525)
593,475
Unsecured debt weighted-average interest
rate/subtotal
3.97
—
650,000
350,000
425,000
700,000
11,550,000
13,675,000
(81,459)
13,593,541
Weighted-average interest rate/total
3.97%
$—
$650,000
$350,000
$425,000
$700,000
$11,550,000
$13,675,000
$(81,459)
$13,593,541
(1)Represents the weighted-average interest rate as of the end of the applicable period, including amortization of loan fees, amortization of debt premiums (discounts), and other bank fees.
(2)Reflects any extension options that we control.
(3)Refer to footnote 3 on the following page.
The following table summarizes our unsecured senior debt and amounts outstanding under our unsecured senior line of credit
and commercial paper program as of September 30, 2025 (dollars in thousands):
Fixed-Rate
Debt
Variable-Rate
Debt
Weighted-Average
Interest
Remaining
Term
(in years)
Total
Percentage
Rate(1)
Unsecured senior notes payable
$12,044,999
$—
$12,044,999
88.6%
3.90%
12.6
Unsecured senior line of credit
and commercial paper program
—
1,548,542
1,548,542
(2)
11.4
4.52
(2)
4.3
(3)
Total/weighted average
$12,044,999
$1,548,542
$13,593,541
100.0%
3.97%
11.6
(3)
Percentage of total debt
88.6%
11.4%
100%
(1)Represents the weighted-average interest rate as of the end of the applicable period, including expense/income related to the amortization of loan fees, amortization of
debt premiums (discounts), and other bank fees.
(2)As of September 30, 2025, we had no outstanding balance on our unsecured senior line of credit and $1.5 billion of commercial paper notes outstanding.
(3)We calculate the weighted-average remaining term of our commercial paper notes by using the maturity date of our unsecured senior line of credit. Using the maturity
date of our outstanding commercial paper notes, the consolidated weighted-average maturity of our debt is 11.1 years. The commercial paper notes sold during the nine
months ended September 30, 2025 were issued at a weighted-average yield to maturity of 4.64% and had a weighted-average maturity term of 17 days.
Issuance and repayment of unsecured senior notes payable
In February 2025, we issued $550.0 million of unsecured senior notes payable, due 2035, with an interest rate of 5.50%.
In April 2025, we repaid our 3.45% unsecured senior notes payable aggregating $600.0 million upon their maturity, using 
proceeds from our February 2025 unsecured senior notes payable offering, with no gain or loss incurred in connection with this
repayment.
$5.0 billion unsecured senior line of credit
As of September 30, 2025, our unsecured senior line of credit, which matures in 2030, including extension options under our
control,  had aggregate commitments of $5.0 billion and bore an interest rate of SOFR plus 0.855%. In addition to the cost of borrowing,
the unsecured senior line of credit is subject to an annual facility fee of 0.145% based on the aggregate commitments outstanding.
Based upon our ability to achieve certain annual sustainability metrics, the interest rate and facility fee rate are also subject to upward
or downward adjustments of up to four basis points with respect to the interest rate and up to one basis point with respect to the facility
fee rate.
Based on certain sustainability metrics achieved in accordance with the terms of our unsecured senior line of credit
agreement, the borrowing rate was reduced for a one-year period by two basis points to SOFR plus 0.855%, from SOFR plus 0.875%,
and the facility fee was reduced by 0.5 basis point to 0.145% from 0.15%. As of September 30, 2025, we had no outstanding balance
on our unsecured line of credit.
$2.5 billion commercial paper program
Our commercial paper program provides us with the ability to issue up to $2.5 billion of commercial paper notes that bear
interest at short-term fixed rates with a maturity of generally 30 days or less and a maximum maturity of 397 days from the date of
issuance. Our commercial paper program is backed by our unsecured senior line of credit, and at all times we expect to retain a
minimum undrawn amount of borrowing capacity under our unsecured senior line of credit equal to any outstanding notes issued under
our commercial paper program. We use the net proceeds from the issuances of the notes for general working capital and other general
corporate purposes. General corporate purposes may include, but are not limited to, the repayment of other debt and selective
development, redevelopment, or acquisition of properties. During the nine months ended September 30, 2025, the commercial paper
notes were issued at a weighted-average yield to maturity of 4.64% and had a weighted-average maturity term of 17 days. As of
September 30, 2025, we had a $1.5 billion outstanding balance on our commercial paper program.
Repayment of secured note payable
In August 2025, we repaid a secured construction loan aggregating $154.6 million with an interest rate of 7.18%, which was
related to our development project at 99 Coolidge Avenue in our Cambridge/Inner Suburbs submarket. In connection with the
repayment, we recognized a loss on early extinguishment of debt of $107 thousand for the write-off of unamortized deferred financing
costs during the three and nine months ended September 30, 2025.
Interest expense
The following table summarizes interest expense for the three and nine months ended September 30, 2025 and 2024 (in
thousands):
Three Months Ended September 30,
Nine Months Ended September 30,
2025
2024
2025
2024
Interest incurred
$140,943
$130,046
$409,603
$379,554
Capitalized interest
(86,091)
(86,496)
(248,579)
(249,375)
Interest expense
$54,852
$43,550
$161,024
$130,179