Short answer

Generally no when it purports to regulate the spouses’ personal duty of fidelity or to impose a private “penalty” for future marital misconduct; such clauses are usually void for being contrary to law, morals, good customs, public order, or public policy. Limited and narrowly crafted agreements that merely settle civil consequences of a past, admitted infidelity (e.g., reimbursement of counseling costs, property adjustments) may be honored if they do not (1) commodify the marital duty of fidelity, (2) stifle a criminal case, or (3) violate family-property rules. The risk of non-enforcement remains high.

Why this is tricky under Philippine law

1) Freedom of contract has limits

Parties are free to contract, but only “so long as they are not contrary to law, morals, good customs, public order, or public policy.” Contracts that violate these limits are void. Liquidated-damages/penal-clause concepts apply only to lawful and contractual obligations—not to duties the law treats as status-based (spousal fidelity).

2) Marriage is a legal status, not a purely private contract

The Family Code treats marriage as an inviolable social institution. Spouses owe each other mutual love, respect, and fidelity by operation of law. Because these are personal and status-based duties, spouses generally cannot predetermine private monetary penalties for their breach. Courts guard against clauses that:

“Price” marital fidelity,
Encourage divorce-like outcomes (which Philippine law does not recognize),
Unduly pressure a spouse to remain or to separate based on money.

3) Criminal-law overlay: adultery/concubinage

Sexual infidelity may amount to crimes (adultery/concubinage), which have their own public consequences. The offended spouse may pardon/condone in certain circumstances, but a bargain whose consideration is “I will not file a criminal case if you pay ₱X” is vulnerable: agreements that stifle prosecution are typically void for being contrary to public policy, and may invite separate criminal or ethical issues.

4) Family-property constraints

Even when spouses voluntarily transfer property after a marital breach, additional rules apply:

Absolute community / conjugal partnership: one spouse generally cannot dispose of community/conjugal property without the other’s consent or appropriate authority. A “penalty” paid from community funds often recycles the injured spouse’s own property back to them—raising validity and fairness problems.
Exclusive property: a transfer from the offending spouse’s exclusive assets is more defensible, but still subject to scrutiny (voluntariness, unconscionability).
Family home: enjoys statutory protections; unilateral “penalty” liens or transfers can be void or require special formalities/consents.
Tax: if the transfer is essentially gratuitous, it can be treated as a donation (donor’s tax implications). If it is damages (to compensate measurable loss), tax treatment differs; documentation and characterization matter.

Common scenarios and how courts are likely to view them

A) Prenuptial clause: “If either spouse cheats, the cheater pays ₱1,000,000.”

Status: High risk of being void. Prenups in the Philippines primarily govern property relations (e.g., separation of property) and cannot validly alter essential marital duties or pre-fix damages for future personal misconduct.

B) Postnuptial “infidelity penalty” (no prior breach)

Status: Similarly void. It tries to regulate future personal conduct by money. It also resembles an unenforceable penalty on a status-based duty.

C) Post-affair settlement that memorializes an admitted past infidelity

Examples: reimbursement of therapy bills; transfer of an exclusive property as part of a compromise of civil claims (e.g., emotional distress under human-relations provisions); written apology; parenting-plan commitments.

Status: Potentially enforceable if carefully structured, but still risky. Key is that it settles past harm, avoids criminal-case suppression, and respects property/tax rules. Courts will examine voluntariness, proportionality, and public-policy concerns.

D) “Pay or I won’t file adultery/concubinage”

Status: Void for being contrary to public policy. Consideration that purchases non-prosecution is defective.

Drafting principles if you consider any agreement (risk-managed approach)

Disclaimer: The following are prudential guidelines; they do not guarantee enforceability.

Do not monetize future fidelity. Avoid language that imposes a fixed sum for future cheating or conditions the marriage on payments.
Address only past, concrete harm. Frame the instrument as a settlement of civil consequences of a past, admitted act (dated, described factually), not as a penalty for a status duty.
Use compensatory, not punitive, remedies. Reimburse documented expenses (medical, therapy, relocation, child counseling, lost earnings), or narrowly tailored property adjustments tied to the harm. Avoid arbitrary large round numbers.
Keep property sources clean. Prefer payment from the offending spouse’s exclusive assets. If community/conjugal assets are involved, obtain written informed consent, consider court approval where appropriate, and avoid impairing creditors or children’s legitime rights.
Respect the family home. Do not assign or encumber it without complying with protective statutes and required consents.
No prosecution bargains. State expressly that the settlement does not purchase non-filing, withdrawal, or suppression of any criminal complaint, and that any decision about a complaint is independent.
Human-relations basis, not “price of fidelity.” If damages are claimed, tie them to the Civil Code’s abuse or acts contrary to morals/good customs provisions (e.g., Articles on human relations), with specific, evidence-based harm.
Voluntariness & fairness. Include acknowledgments that:
- both parties were represented by separate counsel (or knowingly waived it after being advised to obtain one),
- there was no duress, intimidation, or undue influence,
- both had full financial disclosure,
- terms are not unconscionable.
Formalities. Reduce to a public instrument (notarized) for evidentiary weight; record real-property transfers with the Registry of Deeds where applicable; observe titling and tax requirements (documentary stamp tax, capital gains/CGT withholding, or donor’s tax, as the case may be).
Remedies clause. If there is non-payment of a lawful, compensatory sum, provide ordinary contract remedies (interest, attorney’s fees) rather than a fresh “infidelity penalty.”

What courts look for (typical red flags)

Penalty for future misconduct (invalid).
Vagueness (undefined “cheating,” “betrayal,” “inappropriate messaging” without standards or proof thresholds).
Unconscionability (grossly excessive sums vs. actual harm).
Public policy violations (encouraging separation; stifling criminal prosecution).
Improper use of community property without required consent/authority.
Coercion (signed during acute emotional distress without counsel).

Alternatives that are more defensible

Property-regime adjustments via prenup (before marriage): opt for separation of property—lawful and effective. This doesn’t monetize fidelity; it just avoids future disputes.
Post-infidelity civil settlement carefully limited to documented losses and exclusive assets of the offending spouse.
Judicial relief:
- Legal separation (sexual infidelity is a ground), with consequences set by statute (e.g., effects on inheritance, support, custody arrangements, possible damages).
- Civil action for damages under human-relations provisions for particularly egregious, publicly humiliating, or malicious conduct.
- Protection orders (in qualifying abuse contexts) under special laws.

Practical checklist (for counsel and parties)

Identify the nature of the agreement: future penalty (don’t) vs. past-harm settlement (maybe).
Map the asset source (exclusive vs. community) and obtain the right consents.
Itemize actual losses with receipts/records.
Add explicit clause: “This agreement does not constitute or purchase any pardon or non-filing of criminal complaints.”
Confirm independent legal advice for each spouse.
Ensure tax and registration compliance for any transfer.
Avoid public-policy triggers (divorce-like outcomes, commodifying fidelity).

Bottom line

A contract that says, in effect, “Cheating costs ₱X” is very likely void in the Philippines.
A narrow, post-fact settlement compensating provable harm—structured with great care—might be upheld, but is never risk-free.
For durable solutions, use lawful property regimes, or seek judicial remedies the law specifically provides.

This article is for general information only and is not legal advice. Consult a Philippine lawyer to evaluate facts, draft compliant instruments, and manage property/tax consequences.