AAP-First Guidance

Catch-Up Schedule Calculator

Enter the child's age and vaccines already received. Generate a catch-up framework with minimum intervals and next-dose planning for clinical review.

Interval calculator Weeks between two dates. E.g., previous dose → today
Enter both dates to see the interval.

Step 1: Child Information

Preterm or low birth weight Changes the Hepatitis B birth dose and RSV antibody timing

Vaccinate by chronological age, not corrected age. Preterm infants receive vaccines on the same chronological-age schedule as term infants. The documented exceptions are the Hepatitis B birth dose at a birth weight under 2000 g and RSV monoclonal antibody timing.

High-risk medical conditions Sickle cell, asplenia, complement deficiency, HIV and others

These conditions require a modified schedule with additional doses. Selecting them does not change the dose counts below. The tool surfaces the specific deltas to check and links the authoritative CDC table. Do not rely on the general schedule for these children.

Step 2: Vaccines Already Received

Check off each dose the child has received. Enter the date each dose was given where you have it. Dates let the tool apply the age-at-dose rules that decide whether a dose counted and whether another is needed. Leave unchecked if not given or unknown.

Record a combination product Pentacel, Vaxelis, Pediarix, Kinrix, Quadracel, ProQuad, Twinrix

A combination product counts as one dose of each antigen it contains. Recording it here credits every component so the plan does not ask for doses the child already had.

    Verify against the state registry

    A state Immunization Information System (IIS) holds the administered-dose record and is the authoritative history, especially for transfer patients from another state. This tool computes from what you enter; the registry tells you what was actually given.

    Your data never leaves this device. No accounts. No servers. No tracking.

    Frequently Asked Questions About Catch-Up Immunization Schedules

    A catch-up immunization schedule is a plan for children or adolescents who have missed one or more recommended vaccine doses. The AAP catch-up schedule specifies minimum ages, minimum intervals, and age-based dose requirements for each antigen.

    The key principle is that vaccine series generally do not need to be restarted regardless of time elapsed between doses. Previously administered valid doses still count, and the catch-up plan focuses on remaining doses and valid spacing.

    To determine catch-up needs: (1) identify the child's current age; (2) review documented vaccine history to count valid doses by antigen; (3) compare against the AAP-endorsed routine and catch-up schedule; (4) apply minimum interval rules to determine when each remaining dose can be given.

    Important rules: doses given before the minimum age are usually invalid and may need repetition. A 4-day grace period may apply in select scenarios. Some vaccines (for example Hib and PCV) have age-at-first-dose dependent schedules.

    Minimum intervals are the shortest acceptable time between doses of the same vaccine. They ensure adequate immune response. Common examples: DTaP doses 1-3 require a 4-week minimum interval, IPV doses have 4-week minimum intervals between early doses and 6 months before the final dose, and MMR doses require 4 weeks minimum between doses.

    Administering vaccines too close together (shorter than the minimum interval) may reduce the immune response and the dose may be considered invalid. The general ACIP rule: if the interval was at least 4 days shorter than the minimum (the "4-day grace period"), the dose can still be counted as valid.

    Yes. Multiple vaccines can and should be given at the same visit when a child is behind on schedule. This is consistent with AAP recommendations and national immunization administration guidance. Simultaneous administration does not reduce efficacy and is commonly used to accelerate catch-up.

    Some considerations: Live injectable vaccines (MMR, Varicella) not given on the same day should be separated by at least 28 days. Combination vaccines can reduce injection burden. Clinical judgment and local policy still apply.

    When a child starts a series late, the total doses needed may be reduced depending on age at initiation and prior valid doses. For example, a first Hib dose at 15 months or older in a healthy child can complete that series; PCV catch-up can also use fewer doses at older ages.

    AAP-endorsed catch-up guidance applies age-specific rules by antigen, so dose count and interval requirements must be interpreted in context of the child's age and history.

    Because ACIP catch-up validity depends on the age at each dose, not just how many doses were given. A dose count alone cannot answer several routine questions.

    Examples: a Hib dose given at 15 months or older completes the series in a healthy child, while one given at 12-14 months still needs a booster at least 8 weeks later. A MenACWY first dose at 16 years or older needs no booster, while one at 11-12 years does. HPV is a 2-dose series if dose 1 was before the 15th birthday and 3 doses if at 15 or older, decided by the age at dose 1 rather than the current age. An MMR or varicella dose given before the 1st birthday does not count at all.

    Dates are optional. Where a date is missing, the tool says which decision it could not finish instead of guessing.

    Either give them on the same day, or separate them by at least 28 days. There is no valid option in between: two live injectable or intranasal vaccines given 1 to 27 days apart make the second dose invalid, and it must be repeated.

    The rule covers MMR, varicella, MMRV (ProQuad), live attenuated influenza vaccine (LAIV) and yellow fever. It does not apply to live oral vaccines such as rotavirus. The usual 4-day grace period does not apply to this 28-day interval.

    For a first dose at 12-47 months, ACIP prefers separate MMR and varicella injections over combination MMRV because of a higher febrile-seizure risk in that age group.

    Preterm infants are vaccinated by chronological age, not corrected age, at full dose and with no dose reduction. A baby born at 30 weeks gets the 2-month vaccines 2 months after birth.

    The documented exceptions concern hepatitis B and RSV. For a birth weight under 2000 g with an HBsAg-negative mother, the birth dose is deferred to age 1 month or hospital discharge, and a dose given under 2000 g does not count toward the 3-dose series. If the mother is HBsAg-positive or her status is unknown, give hepatitis B vaccine and HBIG within 12 hours of birth regardless of weight; that birth dose still does not count toward the series.

    RSV monoclonal antibody (nirsevimab or clesrovimab) is timed to the RSV season and to gestational age, so confirm eligibility separately.

    Every US state and territory runs an Immunization Information System, a confidential registry of doses actually administered. Well-known examples include NYSIIS (New York), CAIR2 (California), ImmTrac2 (Texas) and MIIC (Minnesota).

    The registry, not a calculator, is the authoritative dose history. It matters most for a transfer patient from another state, where the parent-reported history is often incomplete. Use the state selector on this page to jump to your registry, and check the previous state's registry as well for a recent move.

    School-entry vaccine requirements vary by state, but most states require proof of immunization for DTaP/Tdap (diphtheria, tetanus, pertussis), IPV/OPV (polio), MMR (measles, mumps, rubella), Varicella (chickenpox or evidence of immunity), and Hepatitis B. Many states also require Hepatitis A and Meningococcal vaccines.

    Children who are behind on vaccines can still attend school in most states with a provisional enrollment plan showing they are in the process of catching up. Medical, religious, or philosophical exemptions vary by state. The catch-up calculator helps identify exactly which doses are still needed to meet school entry requirements.