Does the Month You Buy an I Bond Matter?

The month matters; the day inside it does not. A savings bond is issued on the first day of the month you pay for it, and keeps that month’s fixed rate for its whole life.

The I bond calculator takes an issue month rather than a purchase date for exactly this reason. This page explains what the issue month decides and what it does not.

The issue date is the first of the month

TreasuryDirect’s glossary defines the issue date for a savings bond as “the first day of the month in which the Treasury receives funds for the purchase of the security.” Its rates page states the consequence: “I bonds earn interest from the first day of the month you buy them.”

A purchase settled on August 28 therefore carries an August 1 issue date. It earns August’s interest in full, and its twelve-month and five-year marks are counted from August 1.

What the issue month decides	What it does not decide
The fixed rate attached to the bond for life	The semiannual inflation rate, which is the same for every bond in a given period
The months in which the bond’s rate resets	The annual purchase limit, which runs by calendar year
When the 12 months1 lock ends	The minimum purchase, which is $252 in any month

What a rate change does and does not lock

Two components move on different clocks, and confusing them is the most common timing error.

The fixed rate is locked. A bond issued between May and October 2026 carries a fixed rate of 0.90%³ for as long as it exists, whatever Treasury announces later.

The inflation rate is not locked. It is reset every six months for every bond, so buying before an announcement does not preserve the current inflation component beyond the bond’s own next reset. Treasury states that “the date when the rate changes for your bond is every 6 months from the issue date of your bond.”

The practical effect is that a purchase made just before an announcement holds the current composite rate for six months from its issue month, then moves to the newly announced inflation rate. A purchase made just after holds the new composite for its first six months instead.

Buying near a rate announcement

The next announcement is November 1, 2026⁴ (a Sunday; Treasury usually posts on the next business day). Two facts decide what a purchase around that date gets.

First, a payment that Treasury receives in October carries an October issue date, so it takes the fixed rate in force for the May–October 2026 window. Second, a payment received in November carries a November 1 issue date and takes whatever fixed rate is announced for the November 2026–April 2027 window.

Because the fixed rate for that window is not published until the announcement, the comparison cannot be made in advance. The next rate announcement page sets out what is and is not knowable beforehand.

Buying near a year end

The purchase limit is $10,000⁵ per Social Security or Employer Identification Number per calendar year. It resets on January 1 rather than rolling.

A purchase received in December and another received in the following January therefore use two separate annual allowances, even though the two bonds are only a month apart in age. The I bond purchase limit page covers who each limit belongs to.

One caution on late-December purchases. The issue date depends on the month in which Treasury receives the funds, so a payment initiated at the end of December but received in January is a January bond and uses the new year’s allowance.

Does it matter what day of the month I buy an I bond?

Not for interest. The issue date is the first day of the month in which Treasury receives the funds, so a bond bought on the 2nd and a bond bought on the 28th of the same month share an issue date and earn the same interest for that month.

Should I buy before the rate changes?

Buying before an announcement locks the fixed rate in force in your issue month; buying after locks the one announced for the next window. Which is higher cannot be known until Treasury publishes the new fixed rate.

What is my I bond’s issue date?

The first day of the month in which Treasury received payment for the bond. It is shown against each bond in your TreasuryDirect account and is the date every holding-period rule is measured from.

Does buying in December and January use two limits?

Yes. The annual limit is per calendar year, so a December bond and a January bond draw on different years’ allowances.

When does the twelve-month lock start?

On the issue date, which is the first of the purchase month. A bond issued August 1 can first be redeemed on the following August 1, after the 12 months¹ minimum holding period.