Executive Summary

When a child is conceived or born while the mother is married, the law presumes the child to be the legitimate child of the husband, which ordinarily means the child bears the husband’s surname and enjoys the incidents of legitimacy (succession, status, etc.). This presumption is one of the strongest in Philippine law and can be set aside only through a proper court action to impugn legitimacy by the husband (or, in limited instances, his heirs) within strict timelines. Only after legitimacy is defeated can the child be treated as illegitimate—in which case the default surname is the mother’s, with the option to use the biological father’s surname upon acknowledgment and compliance with civil registry rules.

This article explains the legal framework, surname rules, registration procedures, available remedies, and practical pathways.

Core Doctrines and Default Rules

1) Presumption of Legitimacy

A child conceived or born during the mother’s subsisting marriage is presumed legitimate as to the husband.
Effects of legitimacy include: (a) surname of the husband, (b) legitimate filiation to the husband and the mother, (c) rights to support and successional shares as a legitimate child.

2) Who May Challenge and How

Only the husband (and in narrowly defined circumstances, his heirs) may impugn the child’s legitimacy, by filing a court case.
The mother cannot file a case to declare her own child illegitimate to her husband.
The law imposes short, strict prescriptive periods for the husband (or qualifying heirs) to sue; missing these deadlines bars the challenge, no matter the underlying facts. Because these periods are technical and fact-sensitive, immediate counsel is essential.

3) Consequences If Legitimacy Is Not Impugned (or the challenge fails)

The child remains legitimate to the husband and uses the husband’s surname.
The child cannot be registered under the biological father’s surname, and the biological father’s acknowledgment cannot override the presumption or change the surname.

4) Consequences If Legitimacy Is Successfully Impugned

The child is treated as illegitimate (as to the husband). Default surname becomes the mother’s.
The child may use the biological father’s surname if:
1. the biological father acknowledges the child (public document or birth record, as the rules allow), and
2. the parent(s) file the required Affidavit to Use the Surname of the Father (AUSF) or secure a court order if the civil registrar requires it based on the case’s circumstances (see Procedures below).
Using the father’s surname does not deprive the mother of sole parental authority over an illegitimate child; acknowledgment triggers support and allows filiation for legal purposes, but custody remains with the mother unless a court holds otherwise.

Special Situations

A) Mother’s Prior Marriage Is Void Ab Initio

If the mother’s marriage to the husband is later judicially declared void (e.g., psychological incapacity, bigamy), the presumption of legitimacy to that husband may not apply once there is a final court judgment declaring nullity. In practice, civil registrars usually require the final judgment before altering a child’s recorded status/surname. Without that judgment, registrars often still apply the marital presumption.

B) Separation in Fact or Decree of Nullity/Annulment After Conception/Birth

Separation in fact (or even a pending annulment/nullity case) does not by itself defeat the presumption.
If a final decree of nullity/annulment is issued, it may affect future children’s status depending on timing, but it does not automatically change the status/surname of a child already born/registered while the marriage subsisted. Civil registry proceedings or a court petition are typically needed for corrections.

C) Legitimation by Subsequent Marriage

Legitimation generally benefits only children whose parents could have legally married each other at the time of conception. If the mother was still married to another man at conception, the parents were disqualified to marry then; subsequent marriage to the biological father does not legitimate the child under current rules.

Civil Registry & Surname Pathways

Civil registrars apply document-driven rules. The guiding question is: What is the child’s status today, on paper?

1) If the marital presumption stands (no court case or failed impugnation)

Birth Registration: Child is entered as legitimate; surname: husband’s.
Change requests (e.g., to use mother’s or biological father’s surname) are typically denied absent a court order because the child’s legal status is legitimate to the husband.

2) If legitimacy has been judicially impugned (final judgment) or the marriage was declared void (final judgment) and the presumption no longer applies

Default Surname: Mother’s.
Option to Use Biological Father’s Surname: File the AUSF with the local civil registrar if the biological father has acknowledged the child in a manner allowed by law (e.g., in the birth record or a separate public instrument).
Registrars may still require:
- The final judgment (annulment/nullity/impugnation) with certificate of finality;
- Acknowledgment document or joint affidavit;
- For minors, mother’s consent (and often the father’s, if using his surname);
- Supplemental report or petition for correction depending on what’s changing (given name vs. surname vs. status).
Where civil registry rules do not allow an administrative change (because the alteration is substantial—status/filiation), a court petition ( Rule on Civil Registry cases) may be required.

3) Late or Supplemental Entries

If the birth was recorded with incomplete or incorrect data due to the complicated status, parents may file supplemental reports or petitions for correction—administratively for clerical/singular errors; judicially for substantial matters (status, filiation, legitimacy).

Proof and Litigation Notes

1) Evidence to Impugn Legitimacy

Non-access or physical impossibility of sexual relations during the period of conception;
DNA evidence (increasingly decisive when properly obtained and offered);
Other competent proof recognized by rules of evidence. Strict filing periods apply; suits must be filed swiftly once qualifying grounds are known.

2) Evidence to Establish Filiation to the Biological Father (after or independent of impugnation)

Record of birth with the father’s acknowledgment, or
Public instrument (e.g., notarized acknowledgment/admission of paternity), or
Open and continuous possession of status of a child, or
DNA testing consistent with rules of evidence. Establishing filiation to the biological father does not by itself defeat legitimacy to the husband while the presumption stands; the two questions are legally distinct.

Effects on Parental Authority, Support, and Succession

1) If the Child Remains Legitimate to the Husband

Parental authority: jointly with the mother and husband (subject to family law rules).
Support: owed by both legal parents (mother and husband).
Succession: the child is a legitimate heir of the husband.

2) If the Child Becomes Illegitimate (after successful impugnation or where the presumption is inapplicable)

Parental authority: solely with the mother, by default.
Support: owed by both biological parents once filiation to the biological father is established.
Succession: the child becomes an illegitimate heir of the biological father (and of the mother), with the corresponding hereditary share under the Civil Code.

Surname choice (mother’s by default; father’s upon acknowledgment) does not modify parental authority allocations, which are fixed by law unless altered by a court.

Practical Playbooks

A) Mother wants the child to use the biological father’s surname while still married to another man

Assess status: If the child was conceived/born during the subsisting marriage, the marital presumption applies.
Understand the limit: You cannot administratively register the child under the biological father’s surname while the presumption stands.
Legal route: The husband (not the mother) must timely file to impugn legitimacy. Without a successful case, registrars will keep the husband’s surname on record.
After legitimacy is defeated:
- Register/annotate the child as illegitimate;
- Use mother’s surname by default;
- If the biological father acknowledges, file AUSF (or court petition if required) to adopt the father’s surname.

B) Husband believes the child is not his and wants to stop the use of his surname

Act promptly: Consult counsel immediately due to strict deadlines.
Evidence plan: Consider DNA testing and proof of non-access or impossibility.
Reliefs: Petition to impugn legitimacy; upon success, seek civil registry correction/annotation to remove the husband’s surname and adjust status.

C) Biological father wants to acknowledge and have the child use his surname

Coordinate with counsel: If the mother was married at conception/birth, mere acknowledgment cannot defeat the marital presumption.
Post-impugnation/void marriage: If and when the presumption no longer applies (with final judgment), execute the proper acknowledgment and file AUSF; comply with registrar requirements.

Civil Registry Procedures (Typical Documents)

For impugnation/void marriage effects:
- Final judgment (annulment/nullity/impugnation) + certificate of finality;
- Petition or request for annotation in the civil register and PSA records.
For use of biological father’s surname (illegitimate child):
- Acknowledgment by the father (in the birth record or separate public instrument);
- AUSF (Affidavit to Use the Surname of the Father);
- Mother’s consent (if the child is a minor); sometimes father’s consent as well;
- Child’s valid IDs/school records (if applicable);
- Fees and standard civil registry forms;
- If the registrar treats the change as substantial, a court petition may be required.

Frequently Asked Questions

Q1: We’re separated in fact. Can I register my newborn (by my new partner) under his surname? A: If you are still legally married to another man, the marital presumption attaches. Civil registrars will typically require the husband’s surname unless and until there is a final court judgment that removes the presumption for this child.

Q2: Can the biological father sign the birth certificate to put his surname even if I am married to someone else? A: Not to override the marital presumption. His acknowledgment does not displace the husband’s legal paternity while the presumption stands.

Q3: If the husband files late, can he still win? A: The timelines are strict. Filing out of time generally bars the action regardless of evidence. Immediate legal advice is crucial.

Q4: After annulment, can I administratively switch my older child’s surname to the biological father’s? A: Not automatically. You’ll usually need (a) the final decree, (b) proof of filiation/acknowledgment by the biological father, and (c) the appropriate registry process (AUSF or court petition) depending on what’s on the birth record and how substantial the change is.

Q5: Does using the father’s surname give him custody? A: No. For illegitimate children, mother retains sole parental authority unless a court orders otherwise. The father’s acknowledgment creates duties (e.g., support) and rights (e.g., to seek reasonable visitation), but custody remains with the mother by default.

Key Takeaways

If the mother is married, a child born or conceived during that marriage is presumed legitimate to the husband and uses his surname—unless legitimacy is timely and successfully impugned in court.
Acknowledgment by a biological father cannot by itself defeat this presumption.
Once the child is legally considered illegitimate (post-impugnation or where the presumption is inapplicable), the child uses the mother’s surname by default and may opt to use the biological father’s surname upon acknowledgment and compliance with civil registry requirements.
Many changes require final court judgments and formal registry procedures; paperwork, timing, and precise relief sought make or break the outcome.

This article is for general information and does not replace tailored legal advice. For case-specific steps, consult a Philippine family-law practitioner or your local PAO/IBP chapter.