The formula
Slack = Days until due − (Prep + Settlement + Buffer)
Each term is a real consumer of calendar: preparation covers gathering beneficiary details, invoices and any compliance documentation; settlement is the route’s estimated transit (the Settlement Time Estimator decomposes it); the buffer absorbs the unmodelled — a compliance query, a missed cutoff, a correspondent’s holiday.
The buffer deserves respect, not trimming. One business day covers routine friction on established routes; two or more is warranted for first payments to new beneficiaries, unusually large amounts, or corridors with active documentation requirements. Trimming the buffer to zero converts every minor friction directly into a late payment.
How to use this calculator
- 1
Fix the true due date
The date the supplier needs cleared funds — check whether the contract means initiation date or credit date; almost all mean credit.
- 2
Estimate the route’s settlement time
Use the Settlement Time Estimator for the decomposed itinerary: cutoff, hops, destination clearing, calendar.
- 3
Add preparation and buffer
Documentation time on your side, plus at least one business day of buffer — two for new beneficiaries or large amounts.
- 4
Diarise the initiation date
The output is a deadline for you, not for the bank. Put it in the payment run calendar and treat it as the real due date.
Slack as an early-warning system
Run the planner when the invoice arrives, not when it is due — slack is most useful while it is still large. An invoice with 30 days of slack can take the cheapest route available; one with 4 days has its options narrowing by the hour. Treasury teams that compute slack at invoice registration effectively convert late-payment risk into a routing decision made weeks early, when it is free.
Slack also prices route choices rationally. A slower route that saves 0.5% on fees is a good trade at 20 days of slack and a terrible one at 3 — the delay-cost arithmetic (which the Cost of Payment Delay Calculator prices) flips sign as slack shrinks. The planner tells you which regime you are in before you compare quotes.
Recurring payments: schedule the calendar, not each invoice
For monthly supplier payments, payroll or subscription obligations, the back-calculation should run once as policy: fixed initiation days each month, set so that the slowest normal settlement still clears before the due date, with cutoff times annotated. This converts a monthly scramble into a standing payment-run schedule — and makes exceptions visible as exceptions.
The calendar view also exposes structural problems worth fixing: a route whose settlement time regularly consumes most of the available slack is a route to upgrade, and a supplier whose due dates systematically land after weekends is a terms conversation. Payment operations improve fastest when timing data is looked at monthly rather than felt daily.
Common use cases
Invoice registration triage
Compute slack the day an invoice arrives and route it accordingly.
Payment run scheduling
Set standing monthly initiation dates that absorb normal settlement variance.
Deadline feasibility checks
Test instantly whether a route can still meet a close due date before promising a supplier.
Escalation triggers
Define the slack level at which payments escalate to faster routes automatically.
Automate this with the API
Pull the corridor’s indicative settlement timing for the back-calculation.
curl "https://keybs.io/api/v1/tools/settlement?from=NG&to=CN" \ -H "x-api-key: YOUR_FREE_KEY"Free Tools API docs and key registration
Frequently asked questions
How big should the buffer be?
One business day for routine payments on established routes; two or more for first payments to new beneficiaries, unusually large amounts, corridors with heavy documentation requirements, or anything spanning holiday periods. The buffer costs nothing until it is needed; its absence costs a late payment.
What does negative slack actually mean?
That the planned route cannot deliver cleared funds by the due date even if you initiate today. Options in order: a faster route (local payout or instant-rail delivery where available), a partial payment to evidence good faith, or a proactive conversation with the supplier — before the date, when goodwill is still available.
Do due dates mean initiation date or cleared funds?
Almost always cleared funds — "payment received by" language in supplier contracts refers to credit at their account. A payment initiated on the due date over a 3-day route is three days late by the measure that matters. If the contract is ambiguous, clarify it before the first invoice, not after the first dispute.
How do weekends and holidays interact with the planner?
They consume calendar without advancing settlement. Enter settlement time in business days and check the actual calendar window for weekends and holidays in both countries — and the correspondent’s country for wire routes. A "3-business-day" route initiated on a Thursday spans five calendar days at best.
Should I always initiate as late as the plan allows?
No — the latest safe date is a deadline, not a target. Initiating earlier costs float on the funds but buys resilience; initiating at the deadline spends the entire buffer on schedule confidence. Cash-rich businesses should pay early against the plan; cash-tight ones should hold to the deadline deliberately, not accidentally.
How does KeyBS Pay support payment scheduling?
Quotes state the estimated settlement window for the specific route before approval, so the back-calculation uses route-level data rather than a generic "3–5 days". Payment status tracking then confirms progress against the plan. Settlement estimates are route-dependent; the buffer remains your policy.
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